What causes acne, and what makes it worse

Acne is caused by clogged pores. NIAMS, part of the US National Institutes of Health, names three things inside the pore that lead to it: too much oil, a buildup of dead skin cells, and growth of bacteria. Hormones, family history and some medicines set that process off, and a longer list of things, such as stress, too little sleep and oily products, makes existing acne worse. Keeping the two lists apart helps, because you can change many of the things on the second one. It belongs to the 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 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 male sex hormones, and that they increase in both boys and girls 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. The NHS says PMOS used to be called 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.

The guide on 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 a relative with severe acne that left scars raises your own risk of severe acne. Family history is worth telling a doctor.

Medicines

Some medicines can cause acne or make it worse. NIAMS names medicines that contain hormones, corticosteroids and lithium. Corticosteroids are a type of steroid medicine that calms swelling. 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. 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 that it can take 4 to 6 weeks.

The fix the AAD gives is to check labels. Look for "non-comedogenic" or "won't clog pores" on makeup, sunscreen, skin care and hair products. The comedogenic checker looks up the ingredients on a label. 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. Sleep and acne covers what the sources do and do not say about it.
• 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 persistent picking or scratching 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. Smoking and acne explains why the AAD words this as a suggestion rather than a cause.

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 specific diets for treating acne.

The guide does diet cause acne? goes through the research on milk, sugar and chocolate one food at a time. For two foods people often blame, see greasy food and acne and gluten and acne.

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, not from dirt. It says irritating your skin can lead to more breakouts, so scrubbing does harm. And its acne overview 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 around 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 cysts that leave permanent scars.
• 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 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.
• Breakouts that began after starting a new medicine in the last 6 months, one of the signs on the AAD's checklist for seeing a dermatologist.
• Bumps in unusual places such as the armpit, groin or thighs, which the same checklist lists.
• Deep, painful lumps, or spots that leave scars, which the NHS says are a reason to see a GP.

A routine built for the common causes has a gentle cleanser, an acne treatment, a moisturizer and sunscreen. The acne treatment can be one product, or the pair of adapalene and benzoyl peroxide, which the UK NICE guideline lists as a first choice. The complete acne skincare routine lays out each step, and Skinli's photo check can suggest a starting plan from one photo and two questions.