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Introduction

Acne vulgaris is the most common dermatological condition. It is a disorder of the pilosebaceous unit characterised by pustules, papules and comedones. While acne affects most adolescents, some cases may be severe and associated with significant psychosocial impact.

Acne affects 80-90% of adolescents of all ethnicities. There is inconsistent evidence as to the overall prevalence of acne between patients of different ethnicities, but there is an agreement that the clinical presentations and complications of acne may vary between groups (discussed below).2

Men and women are equally affected, although men tend to have more severe symptoms. Acne may present in childhood and persist through adulthood, but these forms of acne are not covered in this article.


Aetiology                          

Acne is a disorder of the pilosebaceous unit (hair follicle and associated sebaceous gland). Increased sebum production (such as due to androgenic hormones), bacterial colonisation (P. acnes) and inflammatory mediators due to innate immune system activation (likely to the presence of bacteria) all play a role.1

Development of acne is multifactorial but is highly heritable particularly among those with severe phenotypes, with up to 80% of patients having a first-degree relative affected.2


Risk factors

Precipitating factors

Acne is typically precipitated by natural hormonal shifts that occur during puberty but may also be precipitated or exacerbated by other hormonal imbalances that lead to excess androgens. This can include endogenous (due to polycystic ovarian syndrome or congenital adrenal hyperplasia), or exogenous (steroids or testosterone) androgens.

Exacerbating factors

Acne may be exacerbated by some medications, including steroids, antiepileptics, and EGRF inhibitors.

Occlusion of the pilosebaceous unit, such as due to topical skin products (including shaving products in men) or cosmetics, may also worsen acne.

There is evidence that diet may impact acne, with high glycaemic index foods (strong association) and dairy (weak association) worsening symptoms, although robust evidence is lacking.

Acne can be exacerbated/caused by chemical exposure. This is known as occupational acne and is seen in factory workers and those handling chemicals such as halogenated aromatic compounds.3

Relieving factors

For some patients, acne may improve with a low-glycaemic load diet. Avoidance of comedogenic cosmetics and products may also improve acne signs and symptoms for some patients.


Clinical features

History

Patients will generally report the onset of acne with early puberty, typically around 12-17 years, but onset may be earlier in some patients.

Female patients may notice cyclical worsening and improvement of symptoms as part of their menstrual cycle.

A thorough history should consider lifestyle factors (diet, skincare and makeup), medications, and family history. It is also important to ascertain what treatments the patient has tried before.

Clinical examination

Acne most commonly affects the face, chest, and upper back, but can affect any skin site with sebaceous glands. Typically, mild (non-inflammatory) acne presents with:

  • Closed comedones: a blocked hair follicle covered by skin (“whitehead”).
  • Open comedones: a blocked hair follicle not covered by skin (“blackhead”).

More severe, inflammatory acne is characterised by:4

  • Papules: small (<1cm), elevated, solid inflammatory lesions that appear erythematous.
  • Pustules: small, well-circumscribed, erythematous epidermal lesions filled with pus (“pimple”).
  • Nodules: similar to papules, but >1cm.
  • Cysts: firm, encapsulated lesions containing fluid or fluid-like material.

After inflammatory acne lesions have healed, there may be remaining signs, including:

  • Scarring: there are many different types of acne scarring including ice pick, box, saucer, anetoderma, atrophic, hypertrophic and keloidal scarring.
  • Pigmented macules: small spots <1cm in diameter, altered in colour, but not usually raised, these fade with time.
  • Keloid scarring: shiny, rubbery nodules of fibrous scar tissue, which may be larger than the original lesion.

Clinical presentations

This article focuses on acne vulgaris, the most common form of acne affecting teens. Other forms of acne (including adult acne, infantile acne and acne that develops in pregnancy) are not specifically covered here.

Clinical presentation may vary depending on patients’ ethnicity. Patients with darker skin may have a lower risk of severe nodulocystic acne than Caucasian patients, but a higher risk of post-inflammatory hyperpigmentation and keloid scarring.2 

Associated conditions

Polycystic ovarian syndrome (PCOS) is the most common endocrinopathy in women, affecting 15-20% of women. It leads to increased thecal ovarian androgen production, and a reduction in sex-hormone-binding protein, leading to an overall increase in free androgens, which exacerbate acne.


Differential diagnoses 

Differential diagnosis Similarities Differences

Acne rosacea

Presents with papules, and sometimes pustules

Affects the face (typically the central face)

Presents with more generalised erythema and occasionally telangiectasias

Tends to affect older women (30s-50s)

 
Rosacea
Figure 5. Rosacea.9

Investigations

Acne is diagnosed clinically, and in most cases does not require any further investigations. If a patient has persistent or unusual acne, skin swab for microscopy and culture may be indicated. If female patients have severe or persistent acne, further testing for underlying hormonal disorders may be required.


Management

Topical therapies

Mild and moderate acne may be sufficiently controlled with topical therapies.

Topical therapies available without a prescription include salicylic acid, a keratolytic that unblocks pores by removing keratin plugs available in many cleansers and other skincare products, and benzoyl peroxide, which has antibacterial effects and is available without a prescription in gel or wash formations at strengths of 2.5-10%.

Tretinoin is a keratolytic that may help to prevent reblocking of pores and can suppress inflammation. It is usually prescribed in low strengths or for use on alternate days, as it can initially be quite irritating to the skin. Although it is a topical treatment, it is still considered teratogenic, and should not be prescribed to women who are trying to conceive, are pregnant or are breastfeeding.10

Systemic therapies

Anti-androgenic options include the oral contraceptive pill and spironolactone. These are options for mild-moderate acne in women.

The oral contraceptive pill (OCP) that is most effective in treating acne contains cyproterone acetate and anti-androgenic progesterone. Although the OCP is effective, it may take more than 6 months for the anti-acne effect to be evident.

Spironolactone is a diuretic and anti-androgen. Although it is prescribed to treat heart failure in both men and women, it is only indicated for the treatment of acne in women. It is contraindicated in pregnancy. 

Antibiotics

Oral antibiotics, such as tetracyclines (doxycycline or minocycline) and erythromycin, can be used to treat moderate acne. They are used for their anti-inflammatory properties in low doses, rather than their antibacterial effects. 

Isotretinoin

Isotretinoin is highly effective at treating moderate to severe acne. It is particularly indicated if acne is persistent, treatment-resistant, cystic or scarring. It markedly reduces sebum production, as well as inflammation, and can induce remission in some patients with acne.

Side effects include mucosal dryness, dry skin, and sensitivity to sun exposure. Regular monitoring of LFTs and cholesterol is also important during treatment with isotretinoin. Like all retinoids isotretinoin is teratogenic and strongly contraindicated in pregnancy.

Other therapies and general management

There are numerous anti-acne products available on the market, some of which are extremely expensive. In general, patients should be advised to choose skincare products that are ‘non-comedogenic’ or ‘non-acnegenic’, including a gentle non-soap cleanser.

General good advice includes maintaining a low glycaemic index diet, and avoiding picking or scratching at acne lesions.


Complications

Post-inflammatory lesions associated with acne, such as scarring and hyperpigmentation, may persist well after the original acne lesion has healed, and in some cases may be permanent. There are many effective treatment options for acne scarring, depending on the lesion, including fillers and laser therapy.10

Acne may also have significant mental health implications, as it can lead to feelings of self-consciousness and low self-esteem. In severe cases, it can be a contributing factor to depression.

It is important to consider this psychosocial burden of acne as part of a holistic assessment.


Key points

  • Acne is the most common dermatological condition, affecting >80% of adolescents. Although it is not harmful, it may have a significant psychosocial impact.
  • The clinical presentation of acne is variable, including open and closed comedones, papules, pustules and cysts. The face, chest, and upper back are typically worst affected.
  • Hormonal shifts that naturally occur during puberty can precipitate acne. Hormonal conditions, such as polycystic ovarian syndrome, can worsen acne.
  • Acne is readily treatable with a variety of effective treatment options available depending on the severity of presentation, including topical and systemic therapies.

Reviewer

Consultant Dermatologist


Editor

Dr Chris Jefferies


References

  1. British Association of Dermatologists. Handbook for Medical Students and Junior Doctors. 2020. Available from: [LINK]
  2. Bhate & Williams. Epidemiology of acne vulgaris. 2012. Available from: [LINK]
  3. Spencer et al. Diet and acne: A review of the evidence. 2009. Available from: [LINK]
  4. DermNet NZ. Acne. 2014. Available from: [LINK]
  5. Wikimedia Commons. Severe upper back acne in a Caucasian woman, showing papules, pustules, and post-inflammatory scarring. Licence: [CC BY-SA]. Available from: [LINK]
  6. DermNet NZ. Facial acne in an East-Asian woman, showing pustules, open and closed comedones, and some scarring. Licence: [CC BY-NC-ND]. Available from: [LINK]
  7. DermNet NZ. Forehead acne in a South-Asian woman, showing post-inflammatory hyperpigmentation. Licence: [CC BY-NC-ND]. Available from: [LINK]
  8. DermNet NZ. Open comedones in a Caucasian woman. Licence: [CC BY-NC-ND]. Available from: [LINK]
  9. Wikimedia Commons. Central face distribution of rosacea. Licence: [CC BY-SA]. Available from: [LINK]
  10. eTG Complete. Acne. 2015. Available from: [LINK]
  11. Australasian College of Dermatologists. Acne scarring. 2020. Available from: [LINK]

 

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