What Causes Acne? An Overview

I’ve been promising a series on acne and rosacea for almost two years, but I’ve had trouble working up enthusiasm for it. The problem is that Pubmed has 12,966 papers on acne and 2,587 papers on rosacea, most of those papers are of poor quality, and it is painful to sift through the dross in search of gold.

Fortunately, Seppo Puusa, who blogs at the Acne Einstein, has offered to help. Seppo’s a very smart guy and I thought a conversation between us about acne and rosacea might be an interesting way to do the series.  Seppo has just written a book called Clear for Life: Science-Based Natural Acne Treatment Program, which looks like a terrific guide to overcoming acne. In this first post in our acne and rosacea series, Seppo gives us his overview of acne. Here’s Seppo!

Does it ever feel like acne is just maddeningly confusing? That it just comes and goes without making any sense? It’s almost as if acne is not one disease but a combination of many diseases. For example one person gets acne from eating gluten, while another claims she can eat whatever she wants but breaks out every time she uses certain skin care products. A third person puts the blame on stress. Another person said zinc supplements helped her to get clear.

Is there a way to make sense of this, to reconcile all these seemingly separate causes? I believe there is. And in this post I’ll do my best to give you a framework for understanding acne. Something that ties all these seemingly separate causes together and helps you to make sense of your acne.

Deconstructing acne

In Tim Ferris’s latest book The Four Hour Chef he explains how to use deconstruction to learn a new skill. Basically you boil the skill down to its bare essentials. In acne these are inflammation and hormones (insulin to be more specific).

Let me start by explaining the pimple formation process. Looking at what happens in your skin is important because, surprisingly, understanding this helps you to understand how diet, gut issues, stress and other things can cause acne. Acne is more than skin-deep, but it still happens at the skin.

In acne, skin cells produce too much keratin, a protein that’s the key structural component of your skin, hair and nails. In the skin it holds skin cells together. Normally as skin cells die they separate and are pushed out of the hair/skin follicle (I’ll just call this a “skin pore” from now on). But the excess keratin makes it harder for the dead cells to separate so they are shed in larger lumps. [1]

These lumps of dead skin cells can block the skin pore, and this block prevents sebum from flowing out. One study showed that acne-prone skin produces about 3 times more sebum than normal skin [2], though other studies have found somewhat smaller differences [3, 4]. Now this torrent of sebum flows into the blocked pore and has nowhere to go. So the skin pore expands, like what happens when you blow into a balloon. Oxygen content drops in the blocked pore, and this helps the bacterium P. Acnes to thrive in the blocked pore [5]. The rest you probably know: the immune system responds and causes inflammation in the area.

This process has two breakpoints — points at which we can intervene to prevent or lessen acne. These are:

  • Excess keratin production
  • Excess sebum production

Counter either, or both, of these and your chances of getting acne go down dramatically. And here is where inflammation and hormones comes into play. Because research shows that inflammation in the skin and hormonal factors are the key drivers in both excessive keratin and sebum production.


Many people think of acne as bacterial disease, but more than anything it’s an inflammatory problem. Many researchers now believe that inflammation in the skin is the trigger that kicks off the whole process. Studies have shown that inflammation is present in the very earliest stages of a pimple, even before P. Acnes bacteria colonizes the skin pore [6, 7]. Cell culture studies also show that inflammatory cytokines increase both sebum and keratin production [1,8]. Finally, several studies have shown that antioxidants, whether topical and supplemental, can be as effective as benzoyl peroxide or antibiotics in treating acne [5,9]; this is consistent with the inflammatory view because oxidative stress can trigger inflammation.


Acne has been conclusively linked to elevated levels of androgens, insulin, and insulin like growth factor 1 (IGF-1). These hormones stimulate sebum production and there’s some research to suggest they also affect keratin production. [1]

The relationship between acne and hormones is quite complicated. Androgens, or male sex hormones, are arguably the primary hormones affecting the skin. It has been shown that acne does not occur in people with inactive androgen receptors in the skin [10].

However, acne patients do not necessarily have higher levels of androgen hormones than people with clear skin. A portion of acne patients seem to have higher levels of some androgen hormones, but this is far from universal. Rather, acne-prone skin seems to be excessively sensitive to androgen hormones.

Insulin and IGF-1 are key hormones in acne. That’s because while androgens mediate lot of the effects on the skin, insulin and IGF-1 are the hormones you have the most control over. I like to call insulin a booster hormone in acne. And where there’s insulin, there’s also IGF-1. That’s why I group these two hormones together. [11]

Insulin and IGF-1 can stimulate sebum production on their own, but they also stimulate the release of androgen hormones from the liver and can increase the skin’s sensitivity to androgen hormones. That’s why studies show low GI diets can help with acne, and why milk can be so bad for the skin. [1, 11]

How sebum production drives antioxidant demand

The skin is the most exposed of all the organs. It’s frequently exposed to UV radiation, ozone from air pollution, bacteria, dust and other ‘inflammatory insults’. So the skin needs constant protection, and that protection comes in the form of antioxidants. In the skin the antioxidants are primarily in sebum. [12]

Research shows a tight correlation between sebum production and vitamin E secretion by the skin [13]. More specifically vitamin E secretion correlates with squalene secretion. Squalene is a fatty acid and a part of sebum. It really looks like the body uses vitamin E to protect squalene in the skin. When squalene oxidizes it turns into squalene peroxide, a highly inflammatory and comedogenic fatty acid. Animal studies show that applying squalene peroxide on the skin causes acne, and the severity of acne is linked to the degree of oxidation of squalene [5].

So the more sebum your skin produces the more antioxidants it requires. There’s good evidence to show that the antioxidant system in acne patients just can’t cope up with this increased demand. For example comparing skin and blood levels of several antioxidants shows significantly lower levels in acne patients than in people with healthy skin. [5, 9]

This is the factor that, I believe, ties together all those seemingly disparate factors that can trigger or relieve acne:

  • Gut problems increase systemic inflammation and deplete antioxidant reserves leading to more acne.
  • Stress triggers the release of neurotransmitters (such as substance P) that can increase inflammation in the skin leading to more acne [1].
  • Diet can induce or relieve inflammation leading to more or less acne. Diet also affects insulin levels.
  • Supplementing with zinc or other nutrients can provide antioxidants which lessen acne [14].
  • Candida and other pathogens in the skin cause local inflammation which can induce acne.


Acne is a very complicated condition and I don’t for one second pretend that this simple framework perfectly explains every case. Individual differences exist, and things get much more complicated when we get down into details. But I do believe it’s a good big picture overview of what causes acne and hopefully clears some confusion surrounding it.

Most importantly, this framework is broadly actionable. It gives you a systematic way to approach acne. Anything you can do to lower insulin and inflammation (both systemic and local in the skin) can help in acne.

Just remember, where there’s insulin there’s oily skin, and where there’s inflammation there’s acne.


  1. Ichiro Kurokawa, et al. New developments in our understanding of acne pathogenesis and treatment. Experimental Dermatology. Volume 18, Issue 10, pages 821–832, October 2009. http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0625.2009.00890.x/full
  2. Harris HH, et al. Sustainable rates of sebum secretion in acne patients and matched normal control subjects. J Am Acad Dermatol. 1983 Feb;8(2):200-3. http://www.ncbi.nlm.nih.gov/pubmed/6219137
  3. S-W. Youn, et al. Does facial sebum excretion really affect the development of acne? British Journal of Dermatology. Volume 153, Issue 5, pages 919–924, November 2005. http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2133.2005.06794.x/full
  4. Apostolos Pappas, et al. Sebum analysis of individuals with and without acne. Dermatoendocrinol. 2009 May-Jun; 1(3): 157–161. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2835908/
  5. Whitney P Bowe, Alan C Logan. Clinical implications of lipid peroxidation in acne vulgaris: old wine in new bottles. Lipids in Health and Disease 2010, 9:141. http://www.lipidworld.com/content/9/1/141
  6. Eady E, et al. Is Acne an Infection of Blocked Pilosebaceous Follicles?: Implications for Antimicrobial Treatment. American Journal of Clinical Dermatology. July/August 2000 – Volume 1 – Issue 4 – pp 201-209. http://adisonline.com/dermatology/Abstract/2000/01040/Is_Acne_an_Infection_of_Blocked_Pilosebaceous.1.aspx
  7. Anthony HT Jeremy, et al. Inflammatory Events Are Involved in Acne Lesion Initiation. Journal of Investigative Dermatology (2003) 121, 20–27; doi:10.1046/j.1523-1747.2003.12321.x. http://www.nature.com/jid/journal/v121/n1/full/5601829a.html
  8. Monica Ottaviani, et al. Lipid Mediators in Acne. Mediators Inflamm. 2010; 2010: 858176. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2943135/
  9. Bowe WP, et al. Acne vulgaris: the role of oxidative stress and the potential therapeutic value of local and systemic antioxidants. J Drugs Dermatol. 2012 Jun;11(6):742-6. http://www.ncbi.nlm.nih.gov/pubmed/22648222
  10. J Imperato-McGinley, et al. The androgen control of sebum production. Studies of subjects with dihydrotestosterone deficiency and complete androgen insensitivity. The Journal of Clinical Endocrinology & Metabolism February 1, 1993 vol. 76 no. 2 524-528. http://jcem.endojournals.org/content/76/2/524.short
  11. Melnik BC, Schmitz G. Role of insulin, insulin-like growth factor-1, hyperglycaemic food and milk consumption in the pathogenesis of acne vulgaris. Exp Dermatol. 2009 Oct;18(10):833-41. Epub 2009 Aug 25. http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0625.2009.00924.x/full
  12. Jens J. Thiele, Swarna Ekanayake-Mudiyanselage. Vitamin E in human skin: Organ-specific physiology and considerations for its use in dermatology. Molecular Aspects of Medicine. Volume 28, Issues 5–6, October–December 2007, Pages 646–667. http://www.sciencedirect.com/science/article/pii/S009829970700057X
  13. Mauro Picardo, et al. Sebaceous gland lipids. Dermatoendocrinol. 2009 Mar-Apr; 1(2): 68–71. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2835893/
  14. Dreno B, et al. Multicenter Randomized Comparative Double-Blind Controlled Clinical Trial of the Safety and Efficacy of Zinc Gluconate versus Minocycline Hydrochloride in the Treatment of Inflammatory Acne vulgaris. Dermatology 2001, Vol. 203, No. 2 http://content.karger.com/ProdukteDB/produkte.asp?Aktion=ShowAbstractBuch&ArtikelNr=51728&ProduktNr=227730

Leave a comment ?


  1. Hi Paul,

    Following my remark about kombucha, I notice some acne breakout since then. I stopped kombucha but neither pounds gained are gone off, nor acne pimples . Could you give some tips to clear this problem ? Can the previous gut flora come to the state it was before this kombucha added ? Thanks !


  2. In the last two years I have discovered that caffeine causes me to have an immediate breakout. Some research indicates that it is pustulated rosacea caused by vasodilation. Have you heard of this? Taking caffeine out of my diet definitely helps.

  3. I am 16 and have suffered from acne since I was 13, but to me it feels like a century since it all began. Being in a mixed (boys and girls) school, I am much happier when it’s vacation, because that way the girls won’t see my face with black spots and inflammations on the cheekbones, right under my eyes. School reopens tomorrow, but I would like to see a dermatologist once more before I start school.

  4. fantastic publish, very informative. I ponder why the other experts of this sector do not realize this.
    You should continue your writing. I am confident, you have a huge readers’ base already!

  5. one thing that really help especially if there´s hormonal aspect to the acne is by nudging your circadian rhythm since CR regulates hormones.
    so, anticipate sunrise, eat early breakfast and all those stuff that important to your CR. Give it a two weeks try…

  6. After suffering with ‘hormonal’ acne for the past year since stopping the contraceptive pill, a friend recommended PHD. I have been trying to follow PHD as closely as possible, plus reducing dairy to a minimum where possible as well as no coffee. So far my skin appears so much better, yes flare ups and break outs come in cycles, so im not sure if im in a ‘good cycle’ at the moment (i hope not). I have the book on order, and can not wait to get down to reading it and understanding more. Im not aiming to lose any weight, but feel so much better having had no wheat or gluten for about 6-8 weeks now.

  7. Thank you, Paul for very informative article. This has helped me a lot and something I can use to heal my acne

  8. very informative and helpful post relating to acne i find PHD very useful source of information

  9. This is one the best explanations on of the how and why’s of acne I’ve seen on the internet. You have both a great knowledge of acne but also the skills necessary to convey them in an easy understand way! 🙂

  10. Great article my understanding of hormones and how they are affecting my skin was invaluable. I have started doing yoga to help with my stress level. I work in a high stress environment. 😆

  11. At NutricianFacts.org it is illuminated how dairy promotes acne.

  12. At nutrician facts .org it is illuminated how dairy promotes acne.

  13. Dr Michael Greger illuminates how dairy promotes acne.

  14. Had always thought that acne breakouts was related to dust and keeping your face clean was the most important. Thanks for your in depth research and letting people like me know about the various causes for acne.

  15. I have spent one hour reading all of the above n I m wondering if all these remedies really work….I have a couple of friends who swear by homeopathy treatment. They say that it tackles acne from the root. I tried it too, but it brought out so much acne to the surface, that I didn’t want to step out of my house. But through your information I learn again to cure my acne and where it comes. Thanks! This is my face today. That’s why I need to get over on it.

  16. Touching face with hands or eating to many candies can cause acne disease.

  17. I used to scrub my face all the time. I learned that by do so caused my acne to get worse. Your paragraph non sebum hit it on the head. All the scrubbing caused my skin to produce more oil.

  18. It is less what to do topically and all about what to do internally. As this article states, insulin type growth factor is a major culprit. Insulin Like Growth factor in milk is what grows a calf to a 600 pound cow in 6 months but promotes acne (especially cheeze) and even cancer in fully grown individuals. There are now tremendous amounts of added hormones in meat as well, but dairy is the mother-load. Educate yourself further at the (not for profit ) site NutricianFacts.org. Type in “acne” under Dr. Greger picture. take an honest tally of all the dairy you are consuming. If you refuse to monitor what you are eating, then you can get Accutane from Canada, it does the job of curing acne forever, but it compromises the kidneys , so more research will be needed in that direction. The greedy lawsuits against Accutane relating it to depression caused this drug to be taken off shelves in US but it is still considered a wonder drug elsewhere.

  19. Paul’s intro to this article talks about it being the first in a series addressing acne and rosacea. This article and most of the comments are about acne. But was there ever a follow-up article about rosacea? if so, I missed it. Would love to see this addressed in-depth similarly. Thank you.

  20. very informative and helpful post relating to acne
    Thank you, Paul

  21. Hello Dr. Jaminet, how are you?

    First I’d like to thank you for the work you do. You are helping people to literally extend their lives. How powerful is that? =)

    I’d like to ask some questions, hope I’m not a bother. I’m a 21 year old guy and since my earliest teenage years I have acne. It’s always been there, not too bad, not too good, but always there. I was a vegetarian from 16 to 19 years old, I don’t remember that having any impact on my acne. I’m not a vegetarian anymore because I discovered paleo and, quite inevitably, low-carb with it. I started eating meat again and soon wanted to follow a strict low-carb protocol. So I ate eggs in the morning, eggs with meat and maybe veggies in lunch and dinner. It was very low-carb, with very occasional slip ups in the weekends. Lo and behold, my acne began to clear up. It was pretty amazing, it was not 100% but I’ve never been that clear. I was happy. Then I had a throat infection, nothing unusual, I have throat infections almost 3 times a year for some 3 years now (don’t know why). At the time I was with the mentality I was invincible due to the new diet. That mentality is not accurate for any diet, but that led me to search a bit more, and I found the “higher” (but for all intents and purposes still low) carb paleo world, along with your site. Not much time after that and I began upping my carb intake. Back came the acne, with a vengeance. I realize that the body is complex, and that there are many things that can affect acne. Here’s what I do nowadays, regarding the things that in my mind may affect acne. The acne, unfortunately, is pretty intense at the moment, to the point that I hurt myself while shaving.

    – I don’t eat breakfast, just lunch and dinner. In my plate I try to make the white rice and the meat portion to occupy the same volume, if that makes sense. I do that because I don’t measure my food in any other way.
    – I wash my face during the shower with regular soap.
    – I take a multivitamin supplement daily (which contains 7 mg of zinc).
    – I take 2 pills (the package recommends 4) of fish oil a day (180g EPA / 120g DHA per pill)

    The questions (sorry for the already too long post)

    1. I read somewhere that I may not be digesting carbs right. My gut seems to be not in the greatest of shapes. I recently tried supplementing with resistant starch, and it turns out that I’m one of the few people who react negatively. It seems that some people have too many bad bugs in the gut, and when you consume resistant starch, it gives you diarrhea and other bad symptoms. It happened to me. I always went to the bathroom to do number 2 only once in 2 or 3 days. My gut really seems to be in bad shape. I was thinking about supplementing with probiotics and after a while try resistant starch again. Do you think it is a good idea? I know that gut health is related with acne.

    2. Do you think the fish oil supplements may be affecting my acne negatively?

    3. Do you think I’m eating too many carbs for PHD purposes?

    4. It seems that my acne is significantly clearer in the morning. That reminded me of circadian rhythms. Do you think strategies for optimizing circadian rhythms (which you describe here) may help?

    I thank you in advance and, again, thanks for your work.

    • Maybe Paul can answer the diet related points, but I’ll just say it’s not a good idea EVER to wash your face with normal soap. Soaps have 2 problems. They are usually formulated with excessively harsh surfactants and end up stripping away most of the protective oils on the skin. The surfactants can also interact with proteins on the skin and cause irritation. Other problem is that they are too alkaline. They increase the skin pH to the point where the skin barrier function weakens.

      All this means is that your skin becomes more sensitive and less able to defend against pathogens and other ‘environmental insults’.

      It’s much better to use facial cleansers. Look for something that’s formulated for sensitive skin – those usually do the least harm.

    • Hi Michel,

      Yes, too much fish oil can be a problem. I don’t think the quantity you are taking is likely to be the issue, but fish oil pills often become rancid and the damaged fish oil is a problem. Don’t take fish oil pills, just eat salmon from time to time.

      No, I don’t think you are eating too many carbs. It’s very unlikely you would do that.

      Circadian rhythms are important.

      You are right that your gut is the main problem. Follow the basic gut healing strategies — vitamin A (liver, spinach, carrots) and vitamin D (sunshine) for immunity, vitamin C, intermittent fasting, circadian rhythm entrainment, etc.

      Also, good nutrition for the skin includes zinc and pantothenic acid. Take our recommended supplements, but extra pantothenic acid.

      Best, Paul

      • I love salmon, and I do eat it from time to time. I’ll stop with the pills.

        I started taking the multivitamin supplement not too long ago, maybe a week or so (it contains vitamins A, D and C). I think it is too early to tell if it’s helping me with my gut or not. I’ll focus more on the other aspects you mentioned. Do you think, then, that probiotics supplement are not necessary if I follow the steps you outlined?

        I’ll see about the pantothenic acid (vitamin B5, right?). If the supplement I’m taking has it (I’m not sure), maybe I’ll double down on the vit. B5.

        Thanks a lot for your answer =)

    • Hi Michel,

      out of curiosity, have you tried any gut testing? Metametrix/Doctor’s Data/BioHealth? I think PHD/Paleo can be a great baseline. I too had a great initial improvement, but then went quickly downhill. The # of things I could eat was narrowing, not widening, and I thought the whole point of this diet is to allow me to start eating different things! but with testing (granted, it costs lots of $), you can know for sure. For example, I had cryptosporidium, and a good deal of my acne improved significantly after treating that.

      I also have a yeast overgrowth, and get pimples when I eat concentrated amounts of glucose or fructose away from a meal. I think the testing can help make sense of symptoms.

      Another anecdote, if it helps? My relative, on the other hand, after going paleo, cleared up nearly all of his skin issues, save for when he eats vegetable oils. He’s even fine eating cookies, croissants, as long as he’s pretty much paleo/PHD-ish. That was a big indicator to me that I had something much more serious going on, despite eating PHD – the liver, bone broth, probiotic foods, lots of vegetables, etc. and shopping almost exclusively organic/local/grass-fed/whatever didn’t solve anything.

      The problem is that the Metametrix stool test didn’t catch things the Organix Acid Test (urinary) did, and neither the Metametrix nor Doctor’s data test caught my H Pylori. So you not only have to test once, but use different tests because no one test is completely comprehensive.

      SCD Lifestyle has a good primer on “Are you wasting money on tests” that I would recommend, and would have saved me a lot of money.

      1) Doctor’s Data Parasitology x 3 (~$250)
      2) BioHealth 401H (~$250?)
      3) Organix Dysbiosis Panel (~$200)

      But also, finding a practitioner who can help with all these results (and accept results from a company they don’t patronize) is key…

      Good luck!


      • Thanks a lot for your reply, LN =)

        I’ll research about this tests, I live in Brazil, I don’t know their availability here. If nothing I’m trying works, I’ll certainly look for professional help, and I will focus on the gut, for I suspect if I go to a dermatologist he will not try to reach the root of the issue.

  22. [ISFP] Skin care - pingback on February 13, 2015 at 5:30 am
  23. What do you think about the use of antibiotics like Oracea to treat type 2 and ocular rosacea? My doctor has made it clear that it will likely be needed longer term. I’m hesitant, but have exhausted everything else.

    • Oracea is just doxycycline. I don’t think it is curative but it is anti-inflammatory and can damp down symptoms. I think PHD works against rosacea – it did against mine and other readers have said so too – but it is a slow recovery.

      • Thanks. I’ve been following the Phd for a couple years with no change. I’m experiencing swelling, and a lot of eye issues, and have tried everything to avoid using doxy. Hate to expose my gut to antibiotics, but feel that I’m left without other options.

      • Paul, can you point us to some of those success stories. I haven’t found them in the book or on the website, and I’d love to hear their experiences and some of the details. I’ve been on PHD for 16 months and I’d say that overall my skin is worse. I’d love to know if there are tweaks that people have found helpful, etc.
        I have tried metro gel — useless, not better or worse.
        I haven’t tried any other pharmaceuticals. I would gladly take a targeted antibiotic to kill an underlying pathogen, etc, but taking one for anti inflammatory properties even at low doses like Oracea doesnt make sense to me unless it also addresses the underlying cause. Everything that I’ve read about it seems to say that for most people, tt has a temporary symptomatic effect while taking it, but not when you stop.
        Kate, if you do decide to try it, please report back. I’d love to know if it helps you.

  24. Hi Paul,

    Is Benzoyl Peroxide a dangerous product to use on the face? I have used for a year or so, in combination with the PHD to achieve really clear skin (type one diabetes also, so lots of factors in play). Hard to know which has worked as I guess I am hiding an important part of my biofeedback by using it. I just wondered the implications of using it long term?

    Thank you.

    • I think benzoyl peroxide is safe. Still, it may disrupt the skin microbiome a little, so I think you should at least experiment with not using it and see if you really need it.

  25. “Many people think of acne as bacterial disease, but more than anything it’s an inflammatory problem.” I guess I have been in the dark as regards that point, but always suspected so. However, bacteria also make implicated in the development of the inflammatory process. 😀

  26. “Finally, a clear breakdown of acne causes! Your overview is informative and insightful, helping us understand the factors behind those pesky breakouts. 👩‍🔬🌟 #AcneInsight”

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