logo Acne

Follicular skin diseases



  • Be able to recognise and manage a straightforward case of acne.

Key points

  • Acne presents with a mixture of non-inflammatory and inflammatory lesions.
  • Acne affects areas where there is greater density of sebaceous glands.
  • Acne is aggravated by genetic and hormonal factors resulting in occlusion of the sebaceous duct.
  • Locally active androgens increase sebum production.
  • Sebum contains a mixture of lipids including cholesterol, glycerides, wax esters and squalene.
  • Bacterial lipases break down triglycerides to produce free fatty acids.
  • Inflammatory mediators from sebaceous duct cells and bacterial enzymes result in rupture of the duct wall.
  • The primary lesion in acne is the comedone, a follicular plug of sebum and keratin.
  • Inflammatory lesions present as erythematous papules, pustules and nodules.
  • Secondary lesions are post-inflammatory erythema, pigmentation and scars.
  • 5-α reductase in the skin converts less active androgens to 5-α testosterone and testosterone.
  • Mild acne should be treated with comedolytic agents. A topical antibiotic may be added.
  • Comedolytic topical agents include benzoyl peroxide,, topical retinoids and azelaic acid.
  • Moderate acne should be treated with comedolytic agent and oral antibiotic and/or oral contraceptive agent.
  • Severe acne and nodulocystic acne should be treated with oral isotretinoin by a dermatologist.
  • Acne fulminans results in fever, arthralgias and malaise. Treatment may require systemic steroids.


Acne is a follicular disorder that mainly affects adolescents but may persist or even become more severe in adulthood. Most, but not all, acne patients have oily skin (seborrhoea).

Usually several types of acne spots appear on the face, but they also may arise on the chest, back and sometimes even more extensively.

Non-inflammatory lesions:

Open comedones

Closed comedones


Inflammatory lesions:

Inflammatory papules

Acne pustules

Inflammatory nodule

Secondary lesions:

Postinflammatory erythema

Postinflammatory pigmentation

Atrophic scars

Pathophysiology of acne

The primary lesion of acne is the comedone, a follicular plug of sebum and keratin.


Sebaceous glands are larger and most numerous on the acne-prone sites i.e. mid-back, forehead and chin. They are also numerous in the ear canal and around the genitals.

Sebum is a complex and variable mixture of lipids including:

Triglycerides produced by sebaceous glands are broken down by bacterial lipases in the sebaceous duct to form free fatty acids.

Sebum has the following functions:

Sebaceous gland cells are stimulated to produce more sebum by androgens. Type 1 5-α reductase in the skin converts less active androgens into testosterone and 5-α testosterone (DHT).

In a fetus, the sebaceous product is a waxy protective layer, vernix caseosa. For 3 to 6 months after birth, sebum resembles that of an adult then it reduces in amount and wax content until the inevitable rise at puberty. In females, oil production is slightly greater in the second half of the menstrual cycle. After the mid-20’s, sebum production declines, particularly after the menopause in females.


Inflammatory mediators include:

Rupture of the duct causes a foreign body granulomatous reaction and releases free fatty acids and sebum into the dermis.

Comedonal acne

Comedones often arise on the forehead and chin. Comedonal acne may be aggravated by:


It may take several months for significant improvement. Suitable topical agents include:

Comedonal acne treated with topical agents

Diathermy to comedones

Comedonal acne treated with isotretinoin

Antibiotics are not usually very effective for this pattern of acne. Persistent or unresponsive comedonal acne warrants referral to a dermatologist for oral isotretinoin. Comedones may also be removed by electrosurgery or microdermabrasion.

Acne vulgaris

Acne vulgaris refers to the common presentation of comedones and superficial inflammatory lesions. Individual spots last up to two or three weeks.

Acne may be considered mild, moderate or severe. Comedones and inflammatory lesions are usually considered separately. The more complex Leeds' grading scale (1 to 12) compares inflammatory lesions with standard photographs.

Mild acne vulgaris

Moderate acne vulgaris

Severe acne vulgaris

Acne severity depends on:


Mild acne vulgaris should be treated with topical agents (see comedonal acne). Topical antibiotics may be added but should not be used alone because of the risk of inducing resistant organisms.

Moderate acne vulgaris should be treated with topical comedolytic agents and oral antibiotics, or in females with no history of or risk factors for thromboembolic disease, the oral contraceptive pill.

The combination pill ethinyl oestrodiol / cyproterone acetate can be used for polycystic ovarian syndrome and resistant acne but compared with other so-called second generation pills has an increased risk of thromboembolic disease.

Patients with longstanding acne, acne that resists treatment or recurs rapidly on discontinuing effective treatment, should be referred to a dermatologist for oral isotretinoin.

Infantile acne

Infantile acne generally affects the cheeks, and sometimes the forehead and chin of newborn babies. It is more common in boys and is usually mild. In most children it settles down within a few months but they may develop troublesome acne at puberty.

Infantile acne

The cause is thought to be fetal hormones.

Treatment is usually with topical agents such as benzoyl peroxide or erythromycin gel. Sometimes, oral antibiotics such as erythromycin, or isotretinoin may be required. NOTE: tetracycline antibiotics should not used because they may cause yellow staining of the developing permanent teeth.

Nodulocystic acne

Nodulocystic acne is a severe form of acne affecting the face, chest and back. It is characterised by multiple inflamed and uninflamed nodules and scarring. It is more common in males. It is known as acne conglobata when there are interconnected abscesses and sinuses; these can cause very severe hypertrophic and atrophic scars.


Patients with nodulocystic acne should consult a dermatologist. The recommended treatment is oral isotretinoin, which should be commenced early to prevent scarring. The treatment is required for at least five months, and further courses are sometimes necessary.

Acne conglobata

Huge nodule

Typical nodules and cysts

When isotretinoin is unavailable or unsuitable, systemic antibiotics, and in women hormonal therapy may also be helpful. Topical treatment is usually ineffective. Individual cysts may shrink with intralesional injections with 2mg triamcinolone acetonide.

Acne fulminans

Acne fulminans is a rare and very severe form of acne conglobata associated with systemic symptoms. It nearly always affects males. It is characterised by:

It is thought to be due to hypersensitivity to P. acnes. Although it mostly just happens, it may be precipitated by:

Acne fulminans

Granulomas and crusted acne lesions

Hypertrophic scarring following acne fulminans


Patients with acne fulminans should consult a dermatologist urgently. Management can prove difficult, and several medications are usually required. These may include:

Topical acne medications are unhelpful.

Hidradenitis suppurativa

Hidradenitis is another form of follicular occlusion syndrome that affects axillae and groins primarily, with submammary and buttock areas involved in some cases. The role of inflamed apocrine glands is uncertain. The result is tender nodules, fluctuant cysts, discharging abscesses, sinuses and scarring.

Hidradenitis results in scarring

Nodules, sinuses and scars

Inflammatory nodules


Hidradenitis is fairly resistant to treatment. Currently, 3-month courses of clindamycin and rifampicin are favoured. The following may also be beneficial: