No, acne is not contagious. However, sharing makeup, brushes, or makeup-applying devices with other people can facilitate the transfer of their acne-causing bacteria onto your skin. This could clog pores and lead to acne breakouts.^[10]

While several hypotheses exist on types of food and nutrients that may worsen acne , there is no clinically confirmed link between nutrition and acne. However, individuals will respond differently to various foods that may impact their symptoms. The following nutritional factors have been shown to have at least some impact on worsening acne symptoms:

• Dairy products: milk, yogurt, ice cream, cheese
• Whey protein or casein protein
• Hyperglycemic or high-glycemic index foods: sugar, sweets, pasta, bread, and soft drinks
• Saturated and trans fat: butter, cream, fried food
• Salt (sodium chloride)^[11]

Acne, or as it is technically called Acne Vulgaris, has historically been linked to dairy (and is the most commonly reported dietary association with acne^[12]).

Acne can be furthered and made worse by excessive insulin secretion^[13] and appears to also be exacerbated by IGF-1^[14] and glucose-dependent insulinotropic polypeptide (GIP). In the case of IGF-1, there are repeated correlations between those with acne and higher serum IGF-1 concentrations.^[15][16]

These systemic factors appear to be induced following dairy consumption with insulin, IGF-1,^[17] and GIP (which acts to further induce insulin^[18]) being increased to levels greater than that of an equicaloric portion of meat (as a comparative protein source).

When looking at serum anabolic factors, dairy protein appears to induce some of these factors to a greater degree than other protein sources

Insulin and IGF-1 both act upon the insulin receptor, the typical signalling pathway includes signalling via PI3K to mTOR/Akt which then induces nuclear ejection of FOX01.^[19]

This nuclear ejection of FOX01 tends to be seen as anabolic, as the presence of FOX01 in the nucleus per se is anti-anabolic and ejection hinders its actions.^[20][21][22] By facilitating anabolic signalling FOX01 ejection can augment androgen-dependent or insulin-receptor (mTOR dependent) anabolism, both the androgen pathway^[23] and the mTOR/Akt pathway (downstream of the insulin receptor)^[24] increase sebaceous lipogenesis (production of lipids in sebocytes, these cells being skin cells that have a high likelihood of acne production) and activation of the mTOR/Akt pathway can augment androgen signalling.^[25]

Anything that activates mTOR/Akt can plausibly increase the efficacy of androgen signalling. Activation of the insulin receptor reliably activates mTOR/Akt (and IGF-1 also acts on this receptor) and is thought to be the main player as there are correlations between diet, insulin and IGF-1 (known to reflect the diet), and acne in humans

Interventions

A few studies have claimed that reducing total insulinogenic secretions of the diet (limiting grains and dairy) would be beneficial in acne control^[26][27] or at least that the link between dairy and acne requires more investigation.^[28][29]

When looking at surveys, there does appear to be an increased risk of acne associated with dairy products although the relative risk ratios (ranging from 1.12^[30]-1.44 depending on dairy product or 1.10-1.19^[31]) appears to be weak.

There is a plausible link between dairy consumption and acne but correlational research does not fully support this link; studies tend to be conducted in adolescents (rather than adults) and the results are not too in favor of a strong link; perhaps weak at best

There appears to be a more reliable link between IGF-1 per se than dairy products per se, and although the latter may spike the former current (limited) research does not support a strong relation between dairy and acne

Dairy By-products?

As both whey protein and casein protein are dairy byproducts, and thus can spike insulin and GIP levels, they are theoretically able to also induce acne.

While many people think that having dirty skin can cause or exacerbate acne symptoms, most of the processes that cause acne actually occur beneath the skin — not on it. For this reason, regular or excessive washing likely has no effect on acne at best and, at worst, may aggravate the skin.^[5]

Stress has been linked to an increase in acne symptoms, but if you don’t already have acne, stress probably won’t cause it. The exact mechanism by which stress increases symptoms of acne is unclear. Our skin cells that produce an oily substance called sebum — which is implicated in acne symptoms — contains receptors for stress hormones. This means that when you’re stressed and overproducing some of these hormones, sebum production and acne may increase. Some studies have shown that acne symptoms increase in college students^[6] and high school students^[7] during high-stress exam periods, but these were only associations and don’t imply that the stress directly led to increased acne.

There isn’t a gene for acne , but if one or both of your parents had acne, you may be more likely to experience this condition. This is because certain genes that influence risk factors for acne, like your inflammatory response and the activity of oil-secreting glands, can be passed down from parent to child.^[8] Research suggests that genetic factors are important in determining your susceptibility to facial acne and the ability of acne-prone hair follicles to evolve into acne-resistant follicles in adulthood.^[9]