The exact cause of acne is mostly unknown. Sometimes when acne in women is due to excess male hormone production, it is diagnosed by an onset of the condition in adulthood; excessive growth of hair, especially in places not usual on a female, called hirsuitism; irregular menstrual cycles; and premenstrual flare-ups of acne.

A 2001 study demonstrated that menstrual cycle does affect acne. Surprisingly, the study revealed that 53% of women over age 33 experienced a higher premenstrual acne rate than women under age 20. Many alternative practitioners assert that acne is
often related to a condition of toxicity in the intestines or liver. This may be due to the presence of bacteria such as Clostridia spp. and Yersinia enterocolitica, a low-fiber diet; a lack of friendly gut flora such as Lactobacillus spp.; an intestinal overgrowth of Candida albicans; and food allergies.
The interaction between the body’s hormones, skin protein, skin secretions, and bacteria determines the course of acne.
Several other factors have also been shown to affect acne

• Age. Teenagers are more likely than anyone to develop acne.
• Gender. Boys have more severe acne and develop it more often than girls.
• Disease. Hormonal disorders can complicate acne in girls.
• Heredity. Individuals with a family history of acne have greater susceptibility to the condition.
• Hormonal changes. Acne can flare up before menstruation, during pregnancy, and menopause.
• Diet. Although they are not the primary cause of acne, certain foods may bring on flare-ups or make the condition worse.
• Drugs. Acne can be a side effect of antibiotics, oral contraceptives, and anabolic steroids.
• Personal hygiene. Use of abrasive soaps, hard scrubbing of the face, or handling pimples will often make them worse.
• Cosmetics. Oil-based makeup and hair sprays worsen acne.
• Environment. Exposure to oils and greases, polluted air, and sweating in hot weather can all aggravate acne.
• Stress. Emotional stress may contribute to acne.
• Friction. Continual pressure or rubbing on the skin by such things as bicycle helmets, backpacks, or tight clothing, as well as hard scrubbing of the skin, can worsen acne.

The most common sites of acne are the face, chest, shoulders, and back, since these are the parts of the body where the most sebaceous follicles are found. In teenagers, acne is often found on the forehead, nose, and chin. As people get older, it tends to appear towards the outer part of the face. Adult women may have acne on their chins and around their mouths. The elderly often develop whiteheads and blackheads on the upper cheeks and skin around the eyes. Inflamed lesions may cause redness, pain, tenderness, itching, or swelling in affected areas.