Contrary to the 2009 study indicated and summarized in another answer, Iodine is a listed cause of acneiform eruptions, iododerma:
This Medscape page says iodine-containing preparations are the cause, yet the advice is that if one has these acneiform eruptions, one should stay away from iodine-containing foods!
As an aside, I hate the classification system for acne and think it is a huge part of the problem with questions like this. Acneiform or acne, what is the difference? Some dermatologists classify acneiform eruptions as acne and others separate them from acne vulgaris.
The terminology used in this field can be complex, and occasionally contradictory. Some sources consider acne vulgaris part of the differential diagnosis for an acneiform eruption. Other sources classified acne vulgaris under acneiform eruption.
4.^ "eMedicine - Acneiform Eruptions : Article by Julianne H Kuflik". http://www.emedicine.com/derm/topic620.htm.
5.^ Acneiform+eruption at the US National Library of Medicine Medical Subject Headings (MeSH)
There is even acne rosacea!
Yet this PubMed Health summary says:
Rosacea is a chronic skin condition that makes your face turn red and may cause swelling and skin sores that look like acne.
So, is rosacea acne or not? The causes are often listed as sun, spicy food, irritating lotions, etc. but the fact is no one really knows what causes rosacea just as no one really knows what causes acne because there are so many different kinds. As well, rosacea and other types of acne often respond to similar treatments as acne - benzoyl peroxide or isotretinoin, but how are they differentiated? The fact that they are prescribed the same treatment seems to indicate that dermatologists have difficulty distinguishing between them as well.
(It angers me that the causes and presentations can be totally different, but there is no difference in name to many dermatological academies, and often no difference in treatment.)
Anyway, back to the question: I think it could also be important to note this paper-
Essentially, in this paper there is data from two different groups. They examine the Kitavans of Papua New Guinea and the Ache hunter-gatherers of Paraguay. Both were systematically examined by doctors trained to diagnose acne. Out of 1,200 Kitavans and 115 Ache of all ages, there was not a single case of acne that was observed.
The conclusion drawn from this paper is that
the astonishing difference in acne incidence rates between nonwesternized and fully modernized societies cannot be solely attributed to genetic differences among populations but likely results from differing environmental factors. Identification of these factors may be useful in the treatment of acne in Western populations.
This paper discusses the diet of the Kitavans:
Tubers, fruit, fish and coconut are dietary staples.
here is the diet of the Ache:
This study looks at the diet of the Ache and suggests that meat was 50% of the diet consumed - heart, liver, all animal organs, and fruits, tubers, even honey.
Cordain et. al make the point that neither of these groups ate what are traditionally considered newly introduced fats - canola or cottonseed oil, soybean oil, corn oil, peanut oil, flaxseed, rapeseed, grapeseed, etc. They ate fat from coconuts (which is saturated!) and animals.
This study of traditional people shows it is clearly possible to eat lots of fat (50% meat!) from animals and not have acne.
The source of fat must be important then, from wild, traditional animals versus seed oils, which are often mechanically and thermally expelled.
I would also draw your attention to the fact that your skin needs both omega-3 and omega-6 fats:
Linoleic acid (18:2omega6) and alpha-linolenic acid (18:3omega3) represent the parent fats of the two main classes of polyunsaturated fatty acids: the omega-6 (n-6) and the omega-3 (n-3) fatty acids, respectively. Linoleic acid and alpha-linolenic acid both give rise to other long-chain fatty acid derivatives, including gamma-linolenic acid and arachidonic acid (omega-6 fatty acids) and docosahexaenoic acid and eicosapentaenoic acid (omega-3 fatty acids). These fatty acids are showing promise as safe adjunctive treatments for many skin disorders,** including atopic dermatitis, psoriasis, acne vulgaris, systemic lupus erythematosus, nonmelanoma skin cancer, and melanoma.** Their roles are diverse and include maintenance of the stratum corneum permeability barrier, maturation and differentiation of the stratum corneum, formation and secretion of lamellar bodies, inhibition of proinflammatory eicosanoids, elevation of the sunburn threshold, inhibition of proinflammatory cytokines (tumor necrosis factor-alpha, interferon-gamma, and interleukin-12), inhibition of lipoxygenase, promotion of wound healing, and promotion of apoptosis in malignant cells, including melanoma. They fulfill these functions independently and through the modulation of peroxisome proliferator-activated receptors and Toll-like receptors.
There is clearly a connection between skin health and the right intake of omega-3 and omega-6 oils. Your body needs both, as the paper above illustrates.
Finally, I draw you to this paper, as one example of why certain fats like omega-3 and omega-6 matter, and how an improper balance of them can cause health problems like acne:
- Increased dietary intake of omega-3-polyunsaturated fatty acids reduces pathological retinal angiogenesis.
Connor KM, SanGiovanni JP, Lofqvist C, Aderman CM, Chen J, Higuchi A, Hong S, Pravda EA, Majchrzak S, Carper D, Hellstrom A, Kang JX, Chew EY, Salem N Jr, Serhan CN, Smith LE.
Nat Med. 2007 Jul;13(7):868-73. Epub 2007 Jun 24.
From the abstract:
These findings indicate that increasing the sources of omega-3-PUFA or their bioactive products reduces pathological angiogenesis. Western diets are often deficient in omega-3-PUFA, and premature infants lack the important transfer from the mother to the infant of omega-3-PUFA that normally occurs in the third trimester of pregnancy. Supplementing omega-3-PUFA intake may be of benefit in preventing retinopathy.
So you might be asking yourself - ok, this is an ophthamology journal. How does this relate to acne?
Well, the key is that angiogenesis, invoked improperly, can also cause rosacea, arthritis, obesity, psoriasis, endometriosis, dementia, and multiple sclerosis.
For example, this study, below, shows a link between angiogensis and rosacea which is relevant because this question concerns skin:
A study of the pathogenesis of rosacea: how angiogenesis and mast cells may participate in a complex multifactorial process.
Aroni K, Tsagroni E, Kavantzas N, Patsouris E, Ioannidis E.
Arch Dermatol Res. 2008 Mar;300(3):125-31. Epub 2007 Dec 11.
Angiogenesis seems to play an important role in the pathogenesis especially of the more severe clinical form of Rosacea. MCs seem to participate in evolution to disease chronicity by contributing to inflammation, angiogenesis and tissue fibrosis."
I should probably explain that angiogenesis is normally invoked during wound healing.
It needs Docosahexaenoic Acid (DHA), which is an omega-3 fatty acid, shown by the paper below.
Gu X et al. Carboxyethylpyrrole protein adducts and autoantibodies, biomarkers for age-related macular degeneration. J Biol Chem. 2003 Oct 24;278(43):42027-35.
They talk about how
Free radical-induced oxidation of docosahexaenoate (DHA)-containing lipids generates ω-(2-carboxyethyl)pyrrole (CEP) protein adducts that are more abundant in ocular tissues from AMD than normal human donors [...] The CEP adduct uniquely indicates oxidative modification from DHA derivatives because CEP protein modifications cannot arise from any other common polyunsaturated fatty acid."
In plain English: CEP, an important component of wound healing and angiogenesis, is produced ONLY by oxidation of DHA (which is an omega-3 fatty acid), not other unsaturated fatty acids. Its abundance depends on DHA abundance, availability of retinyl proteins (i.e Vitamin A), and the level of oxidative stress.
When you add more CEP to a wound, it heals faster. but it needs DHA to happen.
Or to make it easier to understand:
DHA (Omega-3 Fatty Acid) + Vitamin A + oxidative stress = angiogenesis
Oxidative stress can come from stress, not eating right (like not having proper vitamin A, or enough minerals for the body to perform its reactions), not sleeping right, toxin exposure, OR EVEN just every day normal living - going to school, your job, trying to eat well, deal with family, etc.
This recipe is invoked normally and properly during wound healing. You need angiogenesis! But too much or too little of the above items (i.e. too much Omega-3 fat (too much fish for example or supplements) or too much Omega-6 fat/too little Omega-3 (because you eat corn oil, soybean oil, canola oil, etc. - NOTE I am not saying that none of these oils have omega-3, just that they may not have sufficient amounts depending on vitamin A intake and oxidative stress of the body) in the formula can result in health problems like rosacea, your skin, or in your retina, or arthritis. It depends on the composition of your body, your stress, your vitamin and mineral levels.
You could argue rosacea is not acne, yet it is an acneiform eruptions, and clearly, this is one example showing a mechanism for improper fat in diet leading to creation of acneiform eruptions.
Please note that I researched this based on the information provided here, and that Paul Jaminet is the real genius for pulling this information together, not me:
I hope this isn't too confusing. The pathology is not always clear, and I think that's why dermatologists and the internet are full of people who charge $30 for ebooks about how they cleared acne. There can be SO many different causes and pathologies.
But in sum: hunter-gatherers had not a single case of acne on diets of completely in the wild, scavenged and foraged fruits and vegetables or tubers, hunted animals, and/or coconuts, the later two categories which are rather high in saturated fat.
Furthermore, there is a mechanism presented above for the process by which too little or too much omega-3 can cause rosacea, and fairly backed up by researchers.
Finally, in closing, despite what these studies say, attempting to indemnify or completely clear a food from causing acne, there are people who have allergies which can cause skin conditions, per this paper.
This paper discusses eczema, dermatitis herpeformitis and urticaria, stating that food is often an important part.
Thus, just because one study says there is no link to iodine, chocolate, etc. does not mean it is so. I don't accept that answer and neither should this community.
Allergies can take many forms, immediate or delayed, and skin conditions can be one of the many health problems resulting.
I believe that we still have yet to understand the root causes of acneiform eruptions and that those are the real important questions, not listing one study that contradicts another study about what can cause skin conditions.
We need to get away from the mentality does "X" cause acne or "Y" cause acne and start seeing the root of the problem-that there is a process in the body which is imbalanced, and that diet certainly plays an important part, as evidenced by the fact that there were societies in existence completely free of acne.
Please, challenge me though because I honestly just research and research.
Acne is an extremely complex skin condition. Older societies who ate as much as 50% of diet from fresh meat, and even a society that ate many tubers, coconuts, and fish, did not have any incidences of acne. These older societies did not eat flour, vegetable oils, or even beans or other grains.
This provides a strong link between acne and diet.
It is also known and proven that the body and the skin need fat. There is an important biological mechanism for wound healing which requires DHA, an omega-3 fatty acid. Thus insufficient intake of this fat, omega-3 (this is controversial, but while some vegetable oils like canola, soybean, corn, etc. do have some omega-3, it is debatable if it is enough - and again, it depends on the body's needs, personal diets, etc.) or an overabundance of omega-3 (caused, for example by attempting to supplement with omega-3's like fish oil) can cause skin problems, and a mechanism was proposed above to show how this can happen.
If the poster means oily food which has been cooked in substances which do not contain significant amounts of omega-3, there is the possibility that this could cause acne because without omega-3 in the diet in a proper amount, it is possible that excess angiogenesis could occur, causing skin conditions like acne, rosacea, or other inflammatory conditions in the body, which may or may not be visible on the skin.
Concerning saturated fat, the traditional people ate diets varying in composition - one group (Ache) ate a diet of ~ 50% meat, containing considerable saturated animal fat, and the other group (Kitavans) ate more tubers, fish, but also a saturated fat, coconut oil. Thus it seems that one could not necessarily implicate saturated fat with acne.
There are many confounding factors in treating, indeed even naming and properly diagnosing the types of acneiform eruptions, and oily foods are only one of many.