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Acne (Acne Vulgaris)

  • A common skin condition that occurs when the hair follicles get clogged with oil, skin cells, and bacteria
  • Symptoms include blackheads, whiteheads, pimples, and painful nodules under the skin
  • Treatments include lifestyle modifications and medications
  • Involves medical dermatology and pediatric dermatology

Acne (Acne Vulgaris)


Acne, one of the most common skin disorders, peaks in adolescence and early adulthood, affecting around 85% of people between the ages of 12 and 24. Though it is often thought of as a teenage problem, acne can occur in people of any age, though it grows less common as time goes on. Still, over 25% of women and 12% of men in their 40s report having acne.

“It’s a common misconception to think of acne as a teenage disease,” says Yale Medicine dermatologist Christopher Bunick, MD, PhD. “One of the most common reasons adult women between the ages 20 of 40, for example, come to the dermatology clinic is for acne. Clinical trial data revealed that approximately 50% of women in their 20s, 33% of women in their 30s, and 25% of women in their 40s suffer from acne. The good news is there are many treatment options available to help.”

What is acne?

Acne is a category of skin complaints that includes pimples, blackheads, and whiteheads, which can appear on the face, back, and chest.  Pimples that contain pus are known as pustules. Those without pus are called papules. Blackheads and whiteheads are together known as comedones.

Severe cases of acne can cause cysts and nodules to form under the skin and can result in scarring, which can be permanent.

Doctors classify acne based on a number of factors, including the type of lesions (comedones, papules, pustules, etc.) and severity.

  • Comedonal acne. Comedones and a limited number of pustules and papules are present, but without nodules. This type of acne is often called mild acne.
  • Papular, pustular, and non-scarring inflammatory acne. The skin has some comedones, along with a greater number of pustules and papules than are seen in comedonal acne. No nodules, or only a few, are present. This type of acne is also known as moderate acne.
  • Cystic acne and scarring acne. Comedones, more pustules and papules than are seen in moderate acne, as well as nodules and/or cysts are present. Scarring may occur. This type of acne may also be called severe, cystic, or nodulocystic acne.

What causes acne?

Acne develops when hair follicles—the small, tube-shaped cavities near the surface of the skin from which tiny hairs grow—get clogged with oils, dead skin cells, and bacteria.

The oil comes from the sebaceous glands that are connected to the hair follicles under the skin surface. They secrete sebum, an oily substance that travels up the follicle to the surface, where it moisturizes the skin and hair.

Sebaceous glands get their cues to produce sebum from hormones called androgens (one of which is testosterone). When puberty hits, the body increases the production of androgens, which can stimulate the sebaceous glands to produce excess sebum. The excess sebum, along with dead skin cells (which are formed as part of the normal skin cells cycle) clogs hair follicles. Other conditions that cause hormonal changes can trigger acne such as pregnancy, the menstrual cycle (including menopause), and certain medical disorders. Medications that affect hormonal levels, such as oral contraceptives for some women, can also cause acne to flare up.

But bacteria also play a role. Cutibacterium acnes, or C. acnes, is a type of gram-positive bacteria that normally lives on the skin. When the sebaceous glands produce lots of sebum, C. acnes thrives and reproduces, which further clogs the hair follicles and leads to skin inflammation.

The plugged hair follicles can form blackheads and whiteheads. If they become inflamed, red, raised pimples develop on the skin, or nodules or cysts may form under the skin.

What are the risk factors for acne?

Scientists are still working out why acne affects some people, but not others. In addition to fluctuations in the levels of androgens, other factors have been associated with acne:

  • Genetic factors. There is evidence that people with a family history of acne—especially moderate to severe acne—may be more likely to develop it themselves.
  • Diet. Some studies suggest that a high glycemic load diet may contribute to the development or worsening of acne. High glycemic load foods are those that cause blood sugar levels to rise quickly such as white bread, cornflakes, and white potatoes. Other studies have linked the consumption of cow’s milk, particularly skim milk, with acne. More rigorous research studies are needed to fully validate the role of diet in acne vulgaris.
  • Endocrine disorders. Certain endocrine disorders, such as polycystic ovary syndrome and congenital adrenal hyperplasia, can raise androgen levels.
  • Medications and drugs. Various medications and drugs can trigger acne, including corticosteroids and anabolic steroids.
  • Stress. There is some evidence that emotional stress can exacerbate acne.
  • Skin care products. Certain skin care products such as cosmetics, sunscreens, and moisturizers can clog hair follicles, and may play a role in the formation of acne. Many skincare products now report whether they are “non-comedogenic,” meaning they do not exacerbate the formation of comedonal acne.

What are the symptoms of acne?

Acne most frequently occurs on the face, neck, shoulders, chest, and upper back. A person with this condition may notice any or all of the following:  

  • Inflamed, raised bumps (papules)
  • Inflamed, raised bumps with yellow or white tops, filled with pus (pustules)
  • Tiny bumps that may be dark (blackheads) or white (whiteheads)
  • Bumps under the skin that are often painful (cysts or nodules)
  • Darkened spots on the skin that may remain for several weeks or months after acne lesions clear up; this is called “post-inflammatory hyperpigmentation” and is distinct from scarring
  • Scarring, which may appear as indentations, pits, or raised marks

With all of the above, the affected areas may be tender or painful.

While acne is mainly thought of as a skin problem that “only” affects one’s appearance, it often leads to social and mental health issues. People who have acne or the scarring that sometimes follows may be self-conscious, and because of this, may avoid social activities.

How is acne diagnosed?

Doctors will usually begin by asking about your medical history. In particular, they may ask whether you have a family history of acne, take any medications that can affect hormone levels, or use skin care products that may clog hair follicles. Your doctor will also ask about your symptoms and when they began.

A physical exam is essential for diagnosis of acne. Your doctor will look at affected areas of skin to determine the type and severity of acne.

Though a diagnosis of acne can usually be made on the basis of a medical history and physical exam, blood tests are sometimes helpful to measure the levels of hormones (such as testosterone) associated with acne.

How is acne treated?

Acne is usually treated with a combination of lifestyle modifications and medications.

Lifestyle modifications. Some people benefit from changes in their skincare habits, including:

  • Use “non-comedogenic” skincare products (moisturizers, sunscreens, makeup, etc.) These products will not clog pores and are therefore less likely to contribute to acne.
  • Wash affected skin with a gentle soap no more than twice a day.
  • Avoid abrasive cleansers and scrubs.

Medications. Various medications are used to treat acne, including:

  • Benzoyl Peroxide. Available in various strengths with a prescription or over-the-counter, benzoyl peroxide washes, creams, and gels can kill C. acnes, the bacteria associated with acne. It also helps to prevent pores from getting clogged up.
  • Salicylic Acid. This topical medication can help to keep pores from clogging. It is available over-the-counter and as a prescription.
  • Azelaic Acid. Available as a gel or cream, this prescription medication kills bacteria involved in the formation of acne, and reduces the clogging of pores. This particular acne medicine is safe during pregnancy.
  • Antibiotics. Doctors often prescribe topical (lotions, gels, foams) and oral antibiotics to reduce the number of potentially acne-causing bacteria. Frequently used antibiotics include clindamycin, erythromycin, doxycycline, minocycline, and sacrecycline. Antibiotics also have powerful anti-inflammatory properties, which the dermatologist is also taking advantage of when prescribing antibiotics for acne.
  • Topical Retinoids. These creams and gels can help to reduce the clogging of pores. Tretinoin (Retin-A) is one of the most commonly prescribed topical retinoids for acne treatment. They can also help reduce the pigment alterations and scarring caused by acne.
  • Oral Isotretinoin. This oral retinoid is usually reserved for severe cases of acne, cases with scarring, or acne that does not respond to all other therapies. It is particularly effective in treating cystic and nodular acne.
  • Hormonal Therapy. Women with acne may be treated with medications that reduce the level of androgens, such as oral spironolactone.
  • Steroid Injections. To treat severe forms of acne, doctors sometimes inject corticosteroids into acne nodules and cysts to reduce inflammation. Acne scars are treated using a variety of techniques, including dermabrasion, laser therapy, chemical peels, microneedling, and fillers.

What is the outlook for people with acne?

Nearly everyone has experienced acne at some point in their lives, and for most, the outlook is excellent. In general, acne peaks during the teen years and usually clears up on its own in early adulthood. But some people continue to experience acne into adulthood.

In moderate and severe cases, scarring can occur. Fortunately, many treatment options are available that can effectively alleviate symptoms and minimize or remove acne scars.

What is unique about Yale Medicine's approach to treating acne?

“Yale Medicine dermatologists work closely with each patient to tailor an acne care regimen optimized for their particular situation. No two patients are exactly alike, and here at Yale Medicine we strive to take the various factors outlined above, such as gender, age, type of acne, scarring, pigmentation, location of acne—face, chest, back, buttocks, etc.—and other medical conditions into account when we treat patients,” says Dr. Bunick. “This holistic approach to treating acne enhances the doctor–patient relationship and leads to better treatment outcomes for our patients.”