Acne is caused when tiny holes in the skin, known as hair follicles, become blocked.

Sebaceous glands are tiny glands found near the surface of your skin. The glands are attached to hair follicles, which are small holes in your skin that an individual hair grows out of.

Sebaceous glands lubricate the hair and the skin to stop it drying out. They do this by producing an oily substance called sebum.

In acne, the glands begin to produce too much sebum. The excess sebum mixes with dead skin cells and both substances form a plug in the follicle.

If the plugged follicle is close to the surface of the skin, it will bulge outwards, creating a whitehead. Alternatively, the plugged follicle can be open to the skin, creating a blackhead.

Normally harmless bacteria that live on the skin can then contaminate and infect the plugged follicles, causing papules, pustules, nodules or cysts.

Testosterone 

Teenage acne is thought to be triggered by increased levels of a hormone called testosterone, which occurs during puberty. The hormone plays an important role in stimulating the growth and development of the penis and testicles in boys, and maintaining muscle and bone strength in girls.

The sebaceous glands are particularly sensitive to hormones. It is thought that increased levels of testosterone cause the glands to produce much more sebum than the skin needs.

Acne in families

Acne can run in families. If your parents had acne, it's likely that you will also develop it.

One study has found that if both your parents had acne, you are more likely to get more severe acne at an early age. It also found that if one or both of your parents had adult acne, you are more likely to get adult acne too.

Acne in women

More than 80% of cases of adult acne occur in women. It is thought that many cases of adult acne are caused by the changes in hormone levels that many women have at certain times.

These times include:

• periods – some women have a flare-up of acne just before their period
• pregnancy – many women have symptoms of acne in pregnancy, usually during the first three months of their pregnancy
• polycystic ovary syndrome – a common condition that can cause acne, weight gain and the formation of small cysts inside the ovary

Other triggers

Other possible triggers of an acne flare-up include:

• some cosmetic products – however, this is less common as most products are now tested so they don't cause spots (non-comedogenic)
• certain medications, such as steroid medications, lithium (which is often used to treat depression and bipolar disorder) and some anti-epileptic drugs (used to treat epilepsy)
• regularly wearing items that place pressure on an affected area of skin, such as a headband or backpack 
• smoking, which can contribute to acne in older people

Acne myths

Despite being one of the most widespread skin conditions, acne is also one of the most poorly understood. There are many myths and misconceptions about it:

• "Acne is caused by a poor diet." So far, research has not found any foods that cause acne. Eating a healthy, balanced diet is recommended because it is good for your heart and your health in general.
• "Acne is caused by having dirty skin and poor hygiene." Most of the biological reactions that trigger acne occur beneath the skin, not on the surface, so the cleanliness of your skin will have no effect on your acne. Washing your face more than twice a day could just aggravate your skin.
• "Squeezing blackheads, whiteheads and spots is the best way to get rid of acne." This could actually make symptoms worse and may leave you with scarring.
• "Sexual activity can influence acne." Having sex or masturbating will not make acne any better or worse.
• "Sunbathing, sunbeds and sunlamps help improve the symptoms of acne." There is no conclusive evidence that prolonged exposure to sunlight or using sunbeds or sunlamps can improve acne. Many medications used to treat acne can make your skin more sensitive to light, so exposure could cause painful damage to your skin, not to mention increase your risk of skin cancer.
• "Acne is infectious." You cannot pass acne on to other people.