Does whey protein cause acne?

Short answer

Whey itself did not add acne. When 49 people with acne took 30 g a day for 6 months, their acne changed no differently from a no-whey group. The link came from case reports and surveys.

Does whey protein cause acne?
'Milk → whey → acne' — does this formula hold?
Gym talk often says acne showed up right after starting protein shakes. We checked where this idea came from and what happened when people were actually given whey in a trial.
It started with case reports
Acne came after starting whey and faded after stopping
In a report of 5 people whose acne appeared soon after starting whey, 4 cleared up after stopping it, and 1 who restarted saw it come back. Adding another report of 5 people and one of 6 people with acne only on the trunk, 16 cases were reported.
Milk surveys pointed the same way
Milk drinkers had 1.28 times the odds of acne
An analysis that pooled 14 survey studies with 78,529 people found that milk drinkers had 1.28 times the odds of acne compared with people who drank none. At 2 or more glasses a day, it was 1.43 times the odds of people drinking 1 glass a week or less. Whey makes up about 20% of milk protein.
A gym survey went the same way
47% of people with acne took whey
In a survey of 201 gym-goers, 47% of the 100 with acne and 27.7% of the 101 without acne had taken whey supplements in the past 3 months. A study that followed 30 people for 60 days with no comparison group also saw acne appear or worsen while they took supplements.
A trial that split people into groups found otherwise
30 g a day for 6 months did not add acne
In a trial, 49 people with acne were randomly split for 6 months: 25 took 30 g of whey a day (about 1 scoop) and 24 took a supplement without whey. The change in acne counts on the face and trunk did not differ between groups. The only person whose acne got 2 or more grades worse was in the no-whey group.
Surveys mix in other factors
Adjusting for them shrank the difference
In the milk analysis, the difference shrank after adjusting for age, diet and other factors, and there was publication bias, where studies with results are more likely to be published. Gyms also have another factor: steroids. A German review reported acne in about 50% of steroid users.
Bottom line: whey itself did not add acne
Surveys linked them; the feeding trial found no difference
The link between whey and acne came from case reports and surveys. In the trial that randomly gave people 30 g a day for 6 months, acne did not increase. People like the 16 reported cases, whose acne faded after stopping, can compare how their skin does with and without it.