Acne has long been known to cause stress. Now, a new study offers evidence that what has long been suspected — that stress causes acne — may also be true.

Researchers at Stanford put the question to the test by examining students with acne problems on two occasions: once during a relatively stress-free time and again during an exam period. They also administered standardized questionnaires intended to assess stress levels.

The researchers, whose report appears in The Archives of Dermatology, found that ”changes in acne severity correlate highly with increasing stress.”

For people who use acne medicine, the lesson may be to pay close attention to what is going on in their lives, said the senior researcher, Dr. Alexa B. Kimball.

”If they know that a stressful time is coming up,” Dr. Kimball said, ”that’s an important time to be particularly compliant with their medicine.”

Doctors treating acne patients may also want to take stressful conditions into account in deciding when to time a change in prescription, she said.

The findings are based on a study of 22 students — 15 men and 7 women — with serious acne problems. Acne affects 85 percent of the population at some point in life.

Why stress may cause the skin to erupt is unclear. Some research suggests that it may provoke a greater release of hormones associated with acne. The researchers also looked at whether changes in people’s daily lives — in sleep, for example, or eating habits — played a role. Even when these were factored out, the study said, the students’ acne became worse.

The role of stress in acne should not be surprising, Dr. Kimball said. She noted that some acne patients responded well to biofeedback, which is intended to reduce stress. Stress has also been linked to numerous other medical problems and has been shown to affect wound healing.

Just as touching the face can worsen acne symptoms, so can using makeup that contains oil. Lanolin, petroleum jelly, and other oils in oil-based makeup can clog the pores, causing acne outbreaks. Even lipsticks with moisturizers and hair products such as gel and mousse can clog the pores along the lip line and forehead, respectively. Since many people with acne use cosmetics to conceal acne lesions, the oil in these products can be a problem. Therefore, in an effort to hide acne blemishes without worsening their acne, many acne patients use specially labeled, water-based, noncomedogenic makeup. Unlike oil-based makeup, such makeup does not clog the pores. And, in order to keep from spreading oil and bacteria, acne patients should wash their makeup brushes and sponges often.

Unfortunately, even noncomedogenic products sometimes contain a small amount of oil that makes the product easier to apply. This can aggravate acne outbreaks in some patients. In order to test how much oil is in a product, many acne patients place a dab of makeup on a piece of white paper and wait to see if an oil ring forms. The larger the oil ring, the more oil in the product. Many acne patients report being surprised by the size of the oil ring that many popular cosmetics form. But by doing the test, acne patients learn which products they should avoid.

When patients switch from oil-based cosmetics to water-based products, they are usually quite happy with the results. They report water-based cosmetics work well at concealing their complexion flaws and cause fewer acne outbreaks. Beauty and skin care expert Bobbi Brown agrees. “Don’t even think of wearing anything except an oil-free [makeup] formula,”⁵¹ she advises her clients with acne.

Herbs that balance hormone levels are the most commonly prescribed herbs for acne. They include chaste berry, red clover, black cohosh, wild yam, evening primrose, and dong quai, all of which are prescribed for women. These herbs contain phytoestrogen, a plant-based female hormone-like compound. Therefore, although they are useful for women, they are inappropriate for males due to chemical differences in the male and female body.

Herbalists believe phytoestrol increases the effect of the female sex hormone, estrogen, on the body while counterbalancing the effect of androgen. Although studies into the effectiveness of hormone-balancing herbs on acne are limited, many experts think herbs containing phytoestrogen can help women with hormonal acne. Stanley W. Beyrle, a naturopathic doctor at the Kansas Clinic of Traditional Medicine in Wichita, explains:

Black cohosh works as a regulator or a normalizer of the female reproductive system [the part of a woman's body that produces female sex hormones] by helping to restore hormone balance. When it comes to gynecological complaints [conditions such as hormonal acne that involve female sex hormones and sex organs], there isn’t a better herb than black cohosh.