What causes acne? The 3 major reasons why acne occurs

• Acne is caused by excess oil production in your hair follicles, dead skin cells and bacteria in your pores, and an increase in hormonal activity.
• While some of these factors are influenced by genetics, there are also many unhealthy behaviors that can contribute to acne.
• This article was medically reviewed by Mona Gohara, MD, a dermatologist at the Yale School of Medicine.
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Acne affects nearly 50 million Americans each year and is the most common skin condition in the US.

Acne originates from your skin's hair follicles and oil glands, and the most common causes include excess oil, blocked pores, and raised androgen hormones. Here's why.

What causes acne?

Your skin is full of pores. They're tiny openings where hair follicles, sweat, and oil come out. Wherever there's a pore with oil glands, that's where you can get acne, says Sonal Choudhry, MD, a dermatologist at the University of Pittsburgh Medical Center.

The palm of your hands and soles of your feet don't have these glands, so that's why you don't get acne there, says Choudhry. Instead, pores with oil glands are most concentrated on the nose, chin, and cheeks — as well as the back, butt, and shoulders.

Sebum is the name for the oil your skin produces. Sebum's purpose is to keep your skin moist, but too much oil can clog pores, and cause acne. Here's how:

Your hair follicles produce too much oil

The more oil on your face, the more acne you're likely to get, says Noelani Gonzalez, MD, a dermatologist from Mt. Sinai Hospital.

A lot of oil production has to do with genetics — for example, you have a four times higher risk of acne if a first-degree relative has it.

But there are a few behaviors that also lead to increased oil production. "Not washing your face appropriately is one, and that's in terms of frequency and what you're actually using to wash your face," Gonzalez says.

The American Academy of Dermatology recommends washing your face twice a day — once in the morning and again at night. In addition to the standard morning and evening rinses, it's also recommended to wash your face any time after you sweat a lot, like after a workout, or even after wearing a hat or helmet on a sunny day, as sweat can cause bacteria to build up on your skin.

Gonzalez and Choudry agree that having a diet high in refined sugars, like sodas or white breads, can also contribute to acne. A 2016 study found that dairy products and foods high on the glycemic index — candy, sodas, rice milk, cornflake cereals, and even potatoes — can lead to excess oil production and worsen acne. One 2010 study suggests that sugar spikes insulin, which not only leads to an inflammatory response in the body, but also produces oil-causing androgens.

Dead skin cells and bacteria build up in your pores

Propionibacterium acnes, a common bacteria found on the face, can cause acne when combined with oil or dead skin cells. Dead skin cells can accumulate in your pores if you don't wash your face properly, Gonzalez says, and bacteria can eat those skin cells and proliferate in the pores.

"There are these bacteria laying around and now they have been trapped inside with a plug of dead skin cells. That is a perfect recipe for the body to experience inflammation," Choudhry says. Inflammation is when the body rushes white blood cells to an area to fight off an infection. In acne, it's the difference between a blackhead and a pimple, as explained below.

Dirt, oil, and skin cells lead to different forms of acne:

• If a pore is filled with oil and dirt, the top of the pore oxidizes and blackens, leading to blackheads, called comedones.
• If that same pore had skin cells covering it but no inflammation, that's a whitehead.
• Comedones that become inflamed and tender lead to pimples, also called inflammatory acne legion or abscesses. The comedone often fills with pus, which is dead white blood cells that accumulate as a result of your immune system trying to fight off the skin infection.
• Inflammation in the skin that doesn't reach the surface is called cystic acne. It's deep within the hair follicle, and is often quite painful.

Hormonal activity can trigger acne

Androgens are masculinizing hormones — such as testosterone — that increase oil production in the skin. Androgens are higher in males, which is why men get thicker, oilier skin and more hair production. However, women have androgen hormones as well.

When we're kids, we don't have a lot of androgens in our bodies. Once puberty hits, though, our levels of androgens rise and cause our bodies to go through changes. The disrupted hormone levels — in which females produce more estrogen and androgens, and males have heightened testosterone levels — all contribute to acne.

Pregnancy is another time of hormonal disruption. While Gonzalez notes that pregnant women often have dewier skin as a result of high estrogen and progesterone levels during pregnancy (often called "the pregnancy glow"), Choudhry says many people experience acne flare-ups during pregnancy due to increased androgen production. Menopause can also cause acne due to estrogen levels dropping and androgen levels rising.

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