It's estimated as many as 80 per cent of teenagers experience some degree of acne, a condition that makes them feel isolated, diminishes self-esteem and can cause depression.
Acne can begin in adulthood, too, with the majority of cases – 75 per cent – occurring in women.
Many people who've battled acne attest that certain foods aggravate their skin. Yet most dermatologists contend there's no scientific link between diet and acne. The prevailing view is that the food-acne connection is a myth.
Recent studies are, however, challenging this stance. Dairy products and high glycemic foods (e.g. sugary foods and those made from refined flour) have been shown to worsen acne, while omega-3 fats may alleviate it.
Body weight may also play a role. A study published this month in the Archives of Dermatology found that among 3,600 boys and girls, aged 18 and 19, girls who were overweight or obese were twice as likely to have acne as their leaner peers. In boys, there was no link between acne and overweight.
Having a body mass index (BMI) of 25 or greater was associated with acne in girls even after accounting for diet, smoking and mental stress. (BMI is calculated as your weight in kilograms divided by the square of your height in metres. In adolescents aged 18 and older, a BMI of 25 or more signals overweight; 30 more indicates obesity.)
Acne is caused by the combination of too much sebum and a buildup of dead skin cells. (Sebum is an oily fluid secreted by glands in pores to keep skin and hair moisturized.) In teens, rising levels of male hormones, especially testosterone – present in males and females – are thought to trigger acne by creating a surplus of sebum.
Changes in the level of insulin, the hormone that clears sugar from the blood, can also increase the formation of acne.
The link between overweight and acne makes sense to researchers. Insulin and other hormones are often altered in overweight adolescents, increasing the likelihood of acne.
It's also possible that polycystic ovary syndrome could explain some of the findings. It's a hormonal problem that causes women to have symptoms such as irregular menstrual periods, obesity, acne and excess hair growth.
Although diet contributes to weight gain, it's not clear from this particular study if specific foods are to blame.
But other studies have pinpointed certain foods, opposing the notion that diet has nothing to do with acne.
The role of diet in the development of acne wasn't always refuted. Prior to the 1960s, dietary advice was a standard part of acne therapy. At the time, elevated blood sugar and impaired carbohydrate metabolism was implicated in acne. Patients were told to avoid eating too much carbohydrate and too many sugary foods. Dermatology textbooks discouraged foods such as chocolate, sweets, fatty foods and carbonated beverages.
Later, two studies published in 1969 and 1971 – ones that wouldn't be published today – caused doctors to abandon thinking that diet and acne were related. Both studies, fraught with major design flaws, failed to find a link between acne and a handful of foods.
Now, four decades later, researchers are re-examining the diet-acne connection and coming up with evidence that, for certain foods, there is a link.
While there's isn't absolute proof the following dietary factors cause acne, some modifications may be worth considering. And many are all-round healthy suggestions.
High glycemic foods
The most convincing evidence to date has identified high glycemic index (GI) foods as an offender. High GI foods such as white bread, white rice, refined breakfast cereals, cookies, cakes and sugary drinks cause spikes in insulin. This, in turn, limits the production of proteins that attach to testosterone, leaving the hormone free to roam the body and possibly cause acne.
In a recent, well-controlled trial, males aged 15 to 25 who were assigned a low GI diet experienced an improvement in acne, better insulin sensitivity and increases in testosterone-binding proteins in the blood.
Foods with a low GI release sugar more slowly into the bloodstream and don't produce an outpouring of insulin. Examples include grainy breads with seeds, steel cut and large flake oats, 100-per-cent bran cereals, oat bran, brown rice, sweet potatoes, pasta, apples, citrus fruit, grapes, pears, legumes, nuts, yogurt and soy milk.
Two large studies conducted among nine- to 15-year-old children reported a significant association between milk and acne. Kids who drank two or more servings of milk each day were more likely to experience acne compared with those who consumed one or fewer servings a week. In boys, the link was strongest for skim milk.
Researchers speculate that certain components in milk – other than milk fat – may stimulate insulin and growth factors that increase testosterone.
If you do plan to cut back on dairy, get missing nutrients from elsewhere in the diet. Adolescents need 1,300 milligrams of calcium each day for bone health. Plain or unsweetened soy beverages, a good source of calcium and protein, can be substituted for milk. Other non-dairy calcium sources include cooked green vegetables, legumes, almonds, tofu and canned salmon with the bones. A daily calcium supplement may also be required.
There's some evidence to suggest that increasing omega-3 fats may help lessen acne. These fats, plentiful in fatty fish, fish oil supplements and certain plant foods, have anti-inflammatory actions and have been shown to reduce levels of insulin growth factors and inflammation of skin follicles.
Fish rich in omega-3s include salmon, herring, mackerel, trout and sardines. Plant sources of omega-3 fats are flaxseed, flax oil, chia seeds, walnuts and soybeans.
So far, three studies have linked a heavier body weight with a higher rate of acne, although not all of them found the association in both sexes. Regardless of the relationship between weight and acne, it's prudent to maintain a BMI between 18.5 and 25.
Leslie Beck, a Toronto-based dietitian at the Medcan Clinic, is on CTV's Canada AM every Wednesday. Her website is lesliebeck.com.