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Acne: Types, Causes, Prevention & Treatment

All you want to know about acne

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First published: 30.Aug.2023


Acne is a skin condition that mostly affects people in their teens. It is linked to hormonal changes, stress, diet and heredity.

The skin's sebaceous glands produce an excessive quantity of sebum that clogs the pores with the cells that line it. This promotes the growth of bacteria, especially C. acnes and produces inflammation, swelling, and pain. These resolve into blackheads, whiteheads and pimples.

Acne can be treated to heal the skin and suppress the pore clogging process through regular medical therapies involving retinol, antimicrobials and antibiotics or through alternative treatments using diet, tea tree oil or probiotics.

In this Article (Index)

acne and pimples on woman's face

What is Acne?

Acne is an inflammatory skin condition caused by sebum clogged hair follicles. It is quite common, the bacteria in the plugged follicles cause inflammation that can lead to redness, pain, and outbreaks commonly called pimples or zits.

The outbreaks can occur on the face and also on the shoulders, chest and back.

Causes of Acne

The immediate cause is an excess of sebum production in a follicle and a buildup of dead skin cells called keratinocytes that provoke pore clogging and bacterial growth in the pore. See the diagram of the human skin below.

drawing showing each component of the human skin
Human Skin, A. Whittall

The Biology of Acne

The skin has sebaceous glands that produce an oily substance called sebum. These glands are connected to the hair follicle and empty the sebum onto the skin through the follicle's pore.

The follicle is lined with a type of skin cells called keratinocytes and as they age and die, they are shed, rising upwards to the skin's surface. However, when a person has acne, the production of sebum increases (seborrhea), and the sebum and dead keratinocytes stick together inside the pore and clog it. Bacteria that are a normal part of our skin's microbiome, especially Cutibacterium acnes (formerly called Propionibacterium acnes) grow inside these clogged pores producing inflammation and infection.

Finally the follicle's wall breaks down and it bursts, releasing the sebum, skin cells and bacteria into the surrounding dermis provoking the lesions known as pimples.

Types of Acne

The medical name for clogged hair follicles or plugged pors is "comedone". These come in different varieties:

  • Blackheads. (Open comedones) These are plugged follicles that have reached the surface of the skin, opening up. The sebum turns dark in contact with the air as the oil oxidizes, and melanin from the dead cells also tint it black.
  • Whiteheads. (Closed comedones) The plugged hair follicles remain beneath the skin and produce a white lump.
  • Papules. Inflammed follicles, they form small pink bumps that are tender to touch.
  • Pimples (Pustules). The papules evolve into pustules topped with a white-yellowish lesion due to the pus they contain, a mixture of dead white blood cells and bacteria with dead cells and sebum.
  • Nodules. They are solid lesions that can be painful, lodged deeply beneath the skin.
  • Nodular or cystic acne. Pus filled lesions deep beneath the skin.

Severity of acne

Based on the above there are four grades that rank the severity of acne. Ranging from Mild (some open and closed comedones with few papules and pimples) to Severe (many large painful nodules and pustules).

young woman’s face seen from the side with acne on her cheeks, jaw, side of face
Acne. Source

Risk factors for developing acne

There are several factors that increase the risk of developing acne (2).

  • Sex. During adolescense men are more likely to have acne than women. This changes with age: postadolescent women are more affected than men.
  • Geography. People living in towns are more likely to be affected than those living in rural settings.
  • Ethnic origin. Mild acne is more common among the White population and severe forms of acne are more frequent in Asians and Africans.
  • Hormones. Androgens play a role in acne. They are hormones found in men and women and contribute to growth and reproduction. Though usually considered masculine, the female body produces androgens in small ammounts. The best known is testosterone, but there are others.
    During puberty boys and girls produce more androgens and they make the sebaceous glands grow larger and produce more sebum (2).
  • Female Hormones. Polycystic ovarian syndrome, pregnancy and menstruation hormonal changes can also cause acne (2).
  • Family history. Studies suggest that there are genetic factors involve in getting acne. If your parents had it there are more chances that you may get it. Genes influence the type of sebum (more branched fatty acids) in your skin and this has a 50 to 90% chance of being inherited. Three times higher compared to individuals without a family history of the condition (1) (2).
  • Medications, The use of medications such as lithium, steroids, and anticonvulsants can cause acne (1) (2).
  • Age.You can get acne at any age, but it is more predominant among teenagers (35 to 90% of them get it). Acne tends to go away during the thirties.

Factors that can worsen acne

Certain factors can make acne worse (1) (2):

  • Psychological stress. Acne and stress are linked and the mechanism is believed to be hormonal.
  • Diet. Research on food and acne is ongoing. There is some evidence to back the popular notion that eating certain foods can worsen acne. For instance milk, and diets with a high glycemic load are linked to adolescent acne. The cause appears to be the insulin-like growth factor (IGF) a natural hormone found in milk.
    There are no studies supporting the urban myth that eating chocolate worsend acne.
  • Tight clothing. The pressure on the skin affects the pores and this includes pressure from sports helmets, shoulder pads, headbands, underwire brassieres, tight clothes, or backpacks.
  • Environment. Pollution, high humidity, exposure to sunlight.
  • Damaging the skin. Picking or squeezing blackheads and pimples, using harsh soaps and detergents, scrubbing the skin to hard.
  • Using oil based cosmetics. Oils may have a high comedogenic effect (produce pimples), for instance olive oil worsens acne.
  • Insulin resistance. People with insulin resistance tend to have higer levels of IGF and this causes more sebum production. You can take action to improve how your body manages insulin.

Treatment for acne

The objective of the treatment is to heal the existing lesions and prevent others from forming. It takes at least 2 to 3 months for the therapy to be effective. The treatment won't cure acne but it will suppress its nasty effects.

Mild Cases of Acne

A dermatologist will prescribe topical Retinods. These are obtained from vitamin A and they regulate how keratinocytes behave, they make them less cohesive so that they don't clog the pores.

For patients with papules or pustules (red blemishes and pimples), an topical antimicrobial (benzoyl peroxide) or a topical antibiotic may be prescribed such as Clindamycin or Erythromycin. They are usually used together to minimize the risk of antibiotic-resistant bacteria strains emerging.

Women in childbearing ages shouldn't use retionods as they have teratogenic effects and could cause congenital disorders in a developing embryo or fetus (2).

This type of therapy can decrease the number of comedones and lesions by 40% to 70% (3).

For those who can't use retinoids or are intolerant, salicylic acid is an alternative in treating acne (3).

There are more medical therapies for severe cases, involving oral antibiotics, hormonal therapy, surgery, but those are beyond the scope of this article.

Acne Prevention

Although it can't be avoided it can be controlled its effects and recurrence can be improved.

What you put on your skin matters

Touching, picking, squeezing, scrubbing is discouraged not only can it provoke more outbreaks, it can spread infection and cause scarring.

Harsh soaps, detergents, and scrubs should be avoided. Regularly washing one's face with special cleansers with a pH-balancing effect such as salicylic acid or benzoyl peroxide face washes can help. Note however that there is no clear clinical evidence that acne is caused by poor hygene or that frequent face washing stops it from appearing.

Pore clogging lotions and creams should be avoided. Oil-based makeup is not allowed. Only non-comedogenic products such as gels and fluids should be used, including your Sunscreen. Some topical acne treatment products contain sunscreen.

Alternative Therapies for Treating Acne

Herbal therapies such as tea tree oil, plant diets, and probiotics have been tested over the years and some appear to be effective and well tolerated. However, the lack of large scale clinical trials limits the conclusions that can be obtained from them.

Tea Tree oil for acne

There have been several tests involving Tea Tree Oil (TTO).

One single-blind randomized study from 1990 involved 124 participants. They were split into groups using a 5% TTO gel compared to a placebo of 5% benzoyl peroxide lotion to treat mild to moderate acne. The results showed that both treatments "had a significant effect in ameliorating the patients' acne by reducing the number of inflamed and non-inflamed lesions (open and closed comedones), although the onset of action in the case of tea-tree oil was slower." Those using tea tree oil had "fewer side effects" (4).

Another study done in 2007 used tea tree oil gel versus a gel only placebo involving 60 subjects. They applied it externally on their lesions 20 minutes a day for 45 days. The authors reported: "A statistically significant difference was found in favour of tea tree oil gel... For our primary outcome 'Change in acne severity score', there was an improvement in the acne severity index (MD ‐5.75, 95% CI ‐9.51 to ‐1.99, P = 0.003, 60 participants; Analysis 17.2) in the tea tree oil gel group compared with the placebo gel group, from baseline to the end of 45 days of treatment" (5).

Tea tree oil has some side effects but the trial found that itch and burning sensation where the gel was applied was similar in both groups. Only one case in the tea tree group reported minimal scaling.

Acne, Probiotics and the gut microbiome

Probiotics can improve acne as shown by a study in Italy (1987) where the group receiving a supplement with oral probiotics (250 mg of freeze-dried Bifidobacterium bifidum and L. acidophilus) showed greater resolution of acne compared with the non-supplemented group (7).

The effects of probiotics have been known since Robert Silver published in 1961 the first study reporting the benefits of Lactobacilli in controling acne. His trial involved 300 patients (but no control group) who received probiotic supplements with L. acidophilus and Lactobacillus bulgaricus for 16 days. Silver noted that 80% of the patients had a clinical improvement, especially those with severe inflammatory acne. He concluded that the intestinal tract somehow interacted with acne. We now know that the microbiome in our gut modulates our immune system and that oral probiotics regulate the release of inflammatory proteins called cytokines in the skin and that probiotics can affect microbiomes in other parts of the body beyond the gastrointestinal tract (6).

Plant diet and acne

Glycemic Load

A diet with a low-glycemic load helps improve acne.

The glycemic load (GL) is a number that indicates how much a given portion of food will raise blood glucose levels after it is eaten. For instance, one serving of boiled rice (100 g) has a GL of around 20, and 100 g of white bread has a GL of 48 while the same amount of cabbage is less than 1 or 100 g of apples with a GL of 4 (100 g is roughly 3.5 oz. or 1⁄4 lb).

The lower the GL, the lower its impact on raising blood sugar levels. The effect on acne seems to be due to the changes it induces in the gut microbiome and its reduction of insulin levels.

Plant based diets with more insoluble fiber, complex carbohydrates, resistant starch is linked to a lower GL and they improve insulin sensitivity, lower inflammation. They aldo provide prebiotic polysaccharides that boost the gut's mircobiome.

As mentioned further up, high levels of insulin promote the insulin-like growth factor (IGF) that boosts hormone production and keratinocyte growth. A paper reporting these benefits concludes that "Plant-based foods and supplements, especially those rich in fiber and polyphenols, could provide a natural, low-risk intervention for acne vulgaris" (6), one study showed that a low GL diet reduced inflammation and total skin lesion counts (5).

Other Alternative and Complementary Therapies

A systematic review of these alterntive therapies by The Cochrane Collaboration (5) found that pollen bee venom reduces the total amount of skin lesions. It also a lack of evidence to support the use of herbal medicine, acupuncture, or wet-cupping therapy to treat acne.

Vinegar and Acne

Apple Cide Vinegar is promoted in the media as a treatment for acne. We disagree. Visit our page discussing Apple Cider Vinegar as an Acne treatment and the risks involved.

Closing comments

Although acne can't be cured, there are many therapeutical tools to manage the condition. Lifestyle changes such as stress management, healthy diet, and following the therapy for 2 to 3 months can help improve the outcome. There are also alternative therapies with proven effectiveness to treat acne.

References and Further Reading

(1) National Institute of Arthritis and Musculoskeletal and Skin Diseases. (2023). Acne. Last reviewed: July 2023

(2) Sutaria AH, Masood S, Saleh HM, et al. (2023). Acne Vulgaris. [Updated 2023 Aug 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from:

(3) Kraft J, Freiman A.. (2022). Management of acne. CMAJ. 2011 Apr 19;183(7):E430-5. doi: 10.1503/cmaj.090374. Epub 2011 Feb 28. PMID: 21398228; PMCID: PMC3080563

(4) Bassett IB, Pannowitz DL, Barnetson RS. (1990). A comparative study of tea-tree oil versus benzoylperoxide in the treatment of acne. Med J Aust. 1990 Oct 15;153(8):455-8. doi: 10.5694/j.1326-5377.1990.tb126150.x. PMID: 2145499

(5) Cao H, Yang G, Wang Y, Liu J, Smith CA, Luo H, Liu Y. (2015). Complementary therapies for acne vulgaris. Cochrane Database of Systematic Reviews 2015, Issue 1. Art. No.: CD009436. DOI: 10.1002/14651858.CD009436.pub2

(6) Clark AK, Haas KN, Sivamani RK.. (2022). Edible Plants and Their Influence on the Gut Microbiome and Acne. Int J Mol Sci. 2017 May 17;18(5):1070. doi: 10.3390/ijms18051070. PMID: 28513546; PMCID: PMC5454980

(7) Marchetti F, Capizzi R, Tulli A. (2022). Efficacia dei regolatori della flora batterica intestinale nella terapia dell'acne volgare [Efficacy of regulators of the intestinal bacterial flora in the therapy of acne vulgaris]. Clin Ter. 1987 Sep 15;122(5):339-43. Italian. PMID: 2972450

About this Article

Acne: Types, Causes, Prevention & Treatment, A. Whittall

©2023, 30 Aug. 2023. Update scheduled for 30 Aug. 2025.

Tags: acne, probiotics, tea tree oil, Apple Cider Vinegar

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