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^[1]).

Acne can be furthered and made worse by excessive insulin secretion^[2] and appears to also be exacerbated by IGF-1^[3] 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.^[4][5]

These systemic factors appear to be induced following dairy consumption with insulin, IGF-1,^[6] and GIP (which acts to further induce insulin^[7]) 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.^[8]

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.^[9][10][11] By facilitating anabolic signalling FOX01 ejection can augment androgen-dependent or insulin-receptor (mTOR dependent) anabolism, both the androgen pathway^[12] and the mTOR/Akt pathway (downstream of the insulin receptor)^[13] 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.^[14]

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^[15][16] or at least that the link between dairy and acne requires more investigation.^[17][18]

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^[19]-1.44 depending on dairy product or 1.10-1.19^[20]) 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.