Overweight girls in their late teens were twice as likely as their normal-weight peers to report having a lot of acne in a large new survey of Norwegian teenagers that did not find the same link in boys.
Some 3,600 young people in Oslo, aged 18 and 19, provided information on their pimples, weight, diet and other health and lifestyle factors.
Only about a tenth of the girls and 15 per cent of the boys fell into the overweight or obese categories, based on their body mass index (a measure of weight relative to height).
But among the overweight and obese girls, 19 out of every 100 said they had experienced a lot of acne in the past week, compared to 13 of every 100 normal-weight girls who reported recent acne
When the researchers took into account other potential influences, such as diet, smoking and "mental distress," they determined that overweight and obese girls were twice as likely to have acne.
Among the boys, acne afflicted about 14 out of every 100, regardless of weight.
In general, researchers say between 10 per cent and 20 per cent of adolescents experience moderate to severe acne.
Many studies have documented the emotional and social difficulties that go along with the problem, especially during the sensitive teen years.
With a growing number of teens becoming overweight and obese - a circumstance that carries its own social stigma - the Norwegian team writes in the Archives of Dermatology, they wanted to investigate whether there's a connection.
There are physiological factors related to obesity that could explain the Norwegian results, said Dr. Nanette Silverberg, director of pediatric and adolescent dermatology at St. Luke's and Beth Israel Medical Centers in New York and a clinical professor at Columbia University.
For instance, high blood pressure, insulin resistance and hormonal changes, which frequently accompany obesity, "are in the pathway of influence" for acne, said Silverberg, who was not involved in the new study.
"Maybe changes in the level of insulin and other hormones are altered in overweight adolescents, and this can increase the formation of acne," said Dr. Jon Halvorsen, a researcher at Oslo University Hospital who led the study.
Although his results showed a link in girls between being overweight and having acne, they don't prove that one causes the other.
Because the pattern was confined to girls, though, "it is possible that polycystic ovarian syndrome can explain some of our findings," Halvorsen told Reuters Health in an email.
Polycystic ovary syndrome is a condition whose cause is poorly understood but symptoms include too-high levels of male hormones, and often both obesity and acne.
Halvorsen's team couldn't rule out that any of the girls had been diagnosed with the syndrome.
Genetics are also considered important in the development of acne.
Although diet contributes to weight gain, it's not clear that food is to blame for what the researchers found.
When they took into account how many sweets, potato chips and soft drinks the girls usually had, the higher acne rates among overweight girls remained.
"The role of nutrition is controversial, and more studies are needed," Halvorsen said.
Silverberg said there is some evidence from other studies showing that poor diets do contribute to acne.
"Whatever you think is bad for you, eating high-sugar foods, large amounts of carbohydrates, all these things have a negative long term affect on acne. And this is particularly true in the teenage years," she told Reuters Health.