What causes acne, and what makes it worse

Acne has a small number of direct causes and a longer list of things that make it worse. Keeping the two apart helps, because you can change many of the things on the second list. This guide goes through both, using what the American Academy of Dermatology (AAD), the US National Institutes of Health, the NHS and MedlinePlus say. It belongs to Skinli's guide to the types of acne.

What happens inside the pore

Every case of acne begins in a hair follicle, the small tube in the skin that holds a hair and opens at the surface as a pore. An oil gland sits beside each follicle.

NIAMS, part of the National Institutes of Health, names three things inside the pore that lead to acne:

1. Too much oil made in the pore.
2. A buildup of dead skin cells in the pore.
3. Growth of bacteria in the pore.

The NHS describes the same chain in one sentence: hair follicles become blocked with extra oil and dead skin cells, and bacteria can then grow in the blocked follicle and cause swelling and pus.

The AAD adds a useful detail. What clogs the pore decides the type of acne you get. A plug of oil and dead cells alone makes a blackhead or whitehead, the spots described in what acne is. Add bacteria and swelling and you get a pimple. When the swelling goes deep, you get a nodule or cyst. The blackheads vs whiteheads and cystic acne pages cover each end of that range.

Hormones

The AAD says hormones may explain why acne is so common in teenagers. It explains that during puberty, hormones called androgens make the skin's oil glands larger, and the larger glands make more oil, which can clog pores. NIAMS says androgens are often called male sex hormones, and that both boys and girls make more of them during puberty.

Hormone changes later in life matter too. The NHS lists puberty, periods, menopause and pregnancy as times when changing hormone levels can cause acne. MedlinePlus adds birth control pills and stress to that list of hormone-related triggers.

The NHS also names polyendocrine metabolic ovarian syndrome (PMOS) as a condition that can cause acne. Skinli's hormonal acne guide explains that PMOS is the NHS's new name for polycystic ovary syndrome (PCOS). The AAD says women with PCOS usually have other signs of a hormone problem too, such as hair loss on the head, extra hair on the face, or skin that darkens and thickens.

Skinli already has a full guide on this pattern: hormonal acne vs regular acne explains the jawline pattern, the monthly timing, and the treatments doctors use.

Family history

Acne runs in families. NIAMS says you may be more likely to get acne if your parents had it, and MedlinePlus says the problem tends to run in families.

Family history also affects how deep acne goes. The AAD says your risk of deep, painful acne is higher if one of your parents or another close blood relative had deep, painful pimples. It also says the same family history raises the chance of acne scars. Family history is worth telling a doctor.

Medicines

Some medicines can cause acne or make it worse. NIAMS names medicines that contain hormones, corticosteroids (a type of steroid medicine that calms swelling) and lithium. MedlinePlus lists steroids, testosterone, estrogen and phenytoin, a seizure medicine, and says some hormone-releasing birth control devices can make acne worse.

NICE, the UK guideline body, tells doctors to consider whether a medical condition or a medicine is adding to someone's acne, and it names anabolic steroids that people take on their own as an example.

The AAD gives clear advice for this situation: keep taking the medicine and talk with the doctor who prescribed it. Ask whether acne is a known side effect and whether another medicine is possible. Skinli's rule is the same. Never stop a prescribed medicine because of acne without talking to the doctor who prescribed it.

Products you put on your skin and hair

Oil in skin and hair products can clog pores. The NHS lists products that make skin greasy as a cause of acne, and MedlinePlus names greasy or oily cosmetic and hair products as triggers.

The AAD has a name for this: acne cosmetica, meaning acne caused by products put on the skin or hair. Its page on hair products says oily shampoos, conditioners and styling products can cause whiteheads and small bumps along the hairline, the forehead and the back of the neck. It says the acne slowly clears once you stop using the product, and it can take 4 to 6 weeks.

The fix the AAD gives is to check labels. Look for "oil-free", "non-comedogenic" or "won't clog pores" on makeup, sunscreen, moisturizer and hair products. The forehead and chin acne page goes further into hair products, hats and helmets.

Things that make acne worse

NIAMS and the AAD list these as things that can make acne worse:

• Stress. The AAD says stress cannot cause acne but may worsen acne you already have. Its adult acne page explains that the body makes more androgens under stress, and those hormones push oil glands to work harder.
• Too little sleep. The AAD lists getting too little sleep as something that can make acne worse.
• Pressure and rubbing. NIAMS names sports helmets, tight clothes and backpacks. The AAD calls acne from rubbing gear acne mechanica, and MedlinePlus warns against tight headbands and hats.
• Picking and scrubbing. NIAMS lists squeezing or picking spots and scrubbing skin too hard. NICE says that picking or scratching acne often can raise the risk of scarring.
• Pollution and humidity. NIAMS names both as irritants that can make acne worse.
• Smoking. The AAD cites studies finding that smokers are more likely to have acne than non-smokers.

What about food

Food is the most argued-about trigger. MedlinePlus says research does not show that chocolate, nuts or greasy foods cause acne. It says diets high in refined sugar or dairy may be linked to acne in some people, but calls that link controversial. NIAMS says some studies show certain foods may make acne worse, and that research is still going on. NICE advises that there is not enough evidence to support any specific diet for treating acne.

Skinli's guide does diet cause acne? goes through the research on milk, sugar and chocolate one food at a time.

Three facts that clear up common beliefs

The AAD explains that the black color of a blackhead comes from the plug reacting with oxygen in the air. It says scrubbing irritates the skin and can make acne worse. And it states that acne is not contagious, so it cannot be caught from another person.

Causes at different ages

The AAD says people can get acne at almost any age, and the cause often depends on the age:

• Newborns. The AAD says 20 percent of newborns develop neonatal acne, which usually appears between the second and fourth weeks of life and goes away on its own without scars.
• Babies aged 3 to 6 months. The AAD describes infantile acne, which is rare but can cause deep nodules and scars, so it needs a doctor.
• Teenagers. Androgen hormones rise in puberty and enlarge the oil glands, as described above.
• Adults. The AAD says 20 to 40 percent of women with adult acne get it for the first time as adults. Its adult acne page lists changing hormones around periods, pregnancy, perimenopause and menopause, starting or stopping birth control pills, stress, family history, products and medicines as reasons.

How the cause shapes the treatment

Each cause points to a different type of treatment. The AAD's advice is to use the right treatment for each type of spot. For blackheads, it recommends a treatment that unclogs pores, such as adapalene, a retinoid sold without a prescription. For deep, painful acne, it says you need treatment that works on all four causes at once: clogged pores, bacteria, swelling and extra oil, which takes a dermatologist.

When the cause needs a doctor

Most acne comes from the causes above and responds to steady care. Some patterns point to something a doctor should check:

• Acne that appears with irregular periods, extra hair growth, or hair loss on the head, which the AAD links to PCOS.
• Acne that started within 6 months of a new medicine, which the AAD lists as a reason to see a dermatologist.
• Bumps in unusual places such as the armpit, groin or thighs, which the AAD also lists.
• Deep, painful lumps, or spots that leave scars, which the NHS says need a GP.

A routine built for the common causes starts with a gentle cleanser, one active ingredient, a moisturizer and sunscreen. The complete acne skincare routine lays out each step. Skinli's photo check can also suggest a starting plan from one photo and two questions.