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Michael: Imagine waking up the morning of prom, or your wedding day, or a big job interview... and sure enough, you look in the mirror to find your forehead is covered in zits! It’s happened to lots of us.

Acne, or acne vulgaris, is the most common skin disease in humans. It affects about 80% of people at some point in their lives. Most people get acne between the ages of 11 and 30, but sometimes older people continue to struggle with it, too. Acne happens when follicles and pores become clogged with dead skin cells and oils. And... it sucks. But by studying how acne forms, doctors have developed ways to prevent and treat it.

It all starts with your skin: a complex organ made up of two layers and lots of nerves, blood vessels, and glands. Your skin cells regenerate about once a month, so you constantly have dead skin cells sloughing off, and new skin cells rising to the surface. This whole skin-replacement thing isn’t much of a problem, on its own. But lots of these dead skin cells come out through your pores. And pores make things more complicated.

Skin pores are essentially just openings for tiny hairs. Hair follicles, the root ends of the hairs, are embedded in your skin and surrounded by clusters of sebaceous glands, special glands that produce sebum. Sebum is that oily, waxy stuff that comes out of your pores. It helps keep your skin waterproof and moisturized: it keeps excess water out of your body, and it keeps water already inside you from getting out through your skin.

So, sebum is important. But things can go very wrong if your sebum production gets out of whack. When your body doesn’t produce enough sebum, your skin can dry out, making you more susceptible to bacterial or fungal infections. But if your body produces too much sebum, it can build up inside your pores, trap dead skin cells, and cause a blockage.

Increased sebum production is one of the major factors involved in the development of acne. Increased keratin production is another one. Keratin is a protein produced by your hair follicles. It gives structure to each strand of hair, as well as the top layer of your skin. But when the hair follicles produce too much keratin, the extra protein binds together dead skin cells, so they can’t just shed out of the pore like they normally would. You end up with a blockage that then traps more dead skin cells, plus sebum.

Once the pore is officially clogged, it becomes a breeding ground for colonies of bacteria — especially Propionibacterium acnes. That’s a species of commensal bacteria, which basically means it’s friendly. It naturally lives on your skin, and it’s not harmful... most of the time. The commensal bacteria that make up your microbiome probably even help prevent other, more harmful bacteria from colonizing on your skin. So having colonies of Propionibacterium acnes living on you isn’t a bad thing. You want them there — as long as they stay on the surface of your skin.

When the bacteria find their way deep into skin pores where they don’t belong, that’s when they can cause an infection. And infections often cause inflammation. When you get an infection, your immune system responds by increasing blood flow to the area and sending extra immune cells and enzymes to fight off the infection. Different combinations of symptoms cause different kinds of acne, with names you’ve probably heard before: blackheads, whiteheads, pimples, pustules... technically, they all mean different things.

The scientific term for a clogged pore is a comedo, which actually used to mean a parasitic worm. People started using the term to refer to a clogged pore because the stuff that comes out when you squeeze it looks kind of like a worm. When the main symptom is just that the pore is clogged, without much inflammation, that’s either a blackhead or a whitehead. Blackheads are what it’s called when the comedo is open.

The trapped sebum and dead skin cells become oxidized, which turns the surface of the clogged material into a dark color, kind of like how silver tarnishes. When the comedo closes, skin cells grow over the top of the plug and stop this oxidation from happening, so the whitish color of the sebum shows through. That’s called a whitehead.

When there’s a comedo plus an infection that causes inflammation, that’s a different kind of acne: pimples! The typical reddish bumpy kind are more specifically called papules. If the inflammation gets really bad, sometimes the bumps start leaking fluid or bacteria-filled pus. Those kind are categorized as pustules, and they’re usually a much brighter red, or sometimes white from the oozing fluid.

The most severe kind of acne is generally called cystic acne. That’s when the infection takes root in the deepest layers of the skin. Sometimes the infection causes more solid bumps to form, called nodules. And sometimes the infection causes pus-filled bumps, called cysts.

So that’s how acne happens. But what causes it in the first place? What makes healthy pores become clogged, infected, and sometimes ooze-y? Again, there are a few different factors involved.

Genetics seem to be important, for one thing. So if your parents had acne, you’re more likely to have it too. Hormones also have a huge influence on acne — specifically, androgen hormones, like testosterone, which influence the development of both the male and female reproductive systems. Which explains why acne is so much more of a problem during puberty. Androgen hormones are linked to sebum production. So during puberty, when the hormones are highly active, there’s an increase in sebum production. Increased stress has been thought to increase hormone production as well, so if you find yourself breaking out the day before a big test, that’s probably why. When you’re stressed, you produce more hormones, which then increases your sebum production.

Since sebum is an oil, a lot of people say that greasy foods will cause acne. Sometimes you’ll also hear that dairy makes it worse, or even more specific foods, like chocolate. But the truth is, scientists aren’t really sure how or whether diet and acne are connected. There have been lots of studies investigating this, and some do suggest a possible link. But others don’t. We need more comprehensive, controlled trials with plenty of subjects before we can come to any real conclusions.

Doctors do acknowledge that there’s anecdotal evidence, and they say that if changing your diet has helped with your acne, then it makes sense for you to stick with it. There just isn’t enough evidence to support the idea that diet has a role in acne in general. But we do know that exposure to other topical oils, like some cosmetics or moisturizers, can cause acne by blocking your pores with extra oils and trapping sebum.

It’s easy to avoid the problem, though — just look for products that say they’re non-comedogenic, which means that they shouldn’t clog your pores. But the natural oil on your face isn’t really a problem. You’ll often hear that you should wash your face a lot to help prevent acne, but acne isn’t caused by dirt or by the natural oil that’s already on the surface of your skin. And washing your face too much can actually irritate your skin, making acne worse.

To treat acne, the goal is to reduce the factors that come together to cause breakouts. The one thing you shouldn’t do is pop a zit. The big risk is that you’ll push the infection out of the hair follicle and into the surrounding skin, instead of out to the surface. Plus, you’ll irritate the area, causing more inflammation and making the acne take longer to heal. You might also spread bacteria to non-affected pores.

Instead, treatments try to lower sebum production, stop dead cells from clumping together in the pore as much, prevent bacterial growth, and lower inflammation. Treatments can range from mild to aggressive, depending on how severe the symptoms are. For mild acne like blackheads and whiteheads, you can usually use topical over-the-counter medications.

One of the most effective is benzoyl peroxide, a chemical compound that’s really good at killing bacteria. It decomposes into super reactive forms of oxygen, which bind to and destroy the molecules the bacteria need to survive. Another common treatment is salicylic acid, which doesn’t kill the bacteria, but stops them from replicating. It can also break down skin cells and keratin to help unclog the pores.

Inflammatory acne, like papular pimples or cystic acne, sometimes needs stronger treatment to reduce the inflammation. That usually means prescription meds. Antibiotics — the kind that are also used to treat other bacterial infections, from strep throat to urinary tract infections — can be used to treat acne. They stop bacterial growth and reduce inflammation.

Another kind of treatment involves retinoids, which are compounds related to vitamin A. Retinoids work by binding to skin cell receptors to remove dead skin cells and encourage healthy skin cell growth. So retinoids work really well to unclog pores full of dead skin cells. They’re anti-inflammatory, too. In severe cystic acne cases, stronger retinoids actually work at the deeper layers of skin to reduce the size of the oil glands so they produce less sebum.

And since hormones are a big factor in sebum production, using birth control or corticosteroids can regulate female hormones and reduce the amount of androgen hormones being produced. Fewer androgen receptors at work means less sebum production, which means less acne. Sometimes, severe, cystic acne will leave scarring, but there are ways to reduce it.

These procedures don’t necessarily treat or prevent the acne itself, but they can reduce the bumps and scars left over from bad breakouts. Dermabrasion uses a gentle sanding tool to wear down layers of the skin that have scarred over from cystic acne, but it only works for people with lighter skin. This procedure has mostly been replaced by laser resurfacing, which uses laser pulses to remove skin layer by layer until the scar has smoothed out.

Then there are chemical peels, which use compounds like salicylic acid or retinoic acid to perform what’s basically a controlled injury to the top layer of skin, killing the top layer of cells. The dead skin cells peel off, revealing healthy skin cells underneath. Luckily, most people grow out of the acne-ridden years of puberty, though some people will continue to have acne well into their 40s and 50s.

But even though a bad breakout might make you self-conscious, it’s normal, it’s treatable, and it’s not life-threatening. So take care of your skin, talk to your doctor about prescription treatments if you want them, and trust that your acne will probably get better with age. And then you get to look forward to wrinkles!

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