• A person with acne usually presents with a history of troublesome 'spots', most commonly affecting the face, shoulders, back, and chest. The person is most commonly an adolescent or young adult, but acne can occur for the first time in later life.
• Examine all affected areas of skin (including the back and shoulders).
• The skin and hair may have an oily texture and appearance.
• Depending on the severity of the acne, there may be non-inflammatory comedones, inflamed papules or pustules, or a mixture of both.
• Closed comedones (whiteheads) appear as raised bumps on the skins surface, and are skin-coloured or slightly reddened.
• Open comedones (blackheads) have a characteristic black 'plug' caused by oxidised oil and dead skin cells.
• Papules are small, round or oval, inflamed (red), raised elevations of the skin.
• Pustules resemble papules, but have a central pocket of pus.
• Nodules are poorly demarcated swellings that are usually red and tender. They may be fluctuant on palpation. In very severe acne, nodules may track together and form large, deep sinuses (acne conglobata).
• Haemorrhagic acne is caused by bleeding inflammatory lesions, and may be very painful and distressing.
• Look for evidence of scarring and hyperpigmentation.
• Scarring may occur when acne heals, particularly when nodules have been present. It is most commonly atrophic in nature, leading to the formation of 'ice-pick' scars or 'pock marks'.
• Hyperpigmentation may occur after acne resolves, especially in people with darker complexions.
• If the features are atypical of acne vulgaris, consider the possibility of a severe form or clinical variant of acne.
• Images of acne and its clinical variants can be viewed at www.dermnet.org.nz.

[Brown and Shalita, 1998; Thiboutot, 2000; Simpson and Cunliffe, 2004; ICSI, 2006]

• If acne presents with atypical features, consider the possibility of a rarer form of acne.
• Acne conglobata is very severe acne where inflammatory lesions predominate and run together, often accompanied by exudate or bleeding. This form of acne may cause extensive scarring.
• Acne fulminans is a sudden severe inflammatory reaction that precipitates deep ulcerations and erosions, sometimes with systemic effects (such as fever and arthralgia).
• Acne excoriée mainly affects young women and is characterized by self-inflicted wounds. It is primarily a psychological or emotional problem.
• Acne mechanica is caused secondarily to pressure, friction, or rubbing from clothing (such as a mask or hat).
• Acne cosmetica is caused by contact of the skin with comedogenic products.
• Chloracne is caused by occupational exposure to halogenated hydrocarbons. It is characterized by the presence of numerous, large comedones.

Recommendations for the diagnosis of acne vulgaris and its clinical variants are based on an international guideline [ICSI, 2006] and expert opinion from narrative reviews [Brown and Shalita, 1998; Thiboutot, 2000; Wolf, 2002; Simpson and Cunliffe, 2004].

• Acne vulgaris is rarely misdiagnosed. Conditions which may mimic the signs of acne include:
• Rosacea is the condition most commonly mistaken for acne vulgaris. It usually occurs in older people and its main symptom is flushing and the presence of inflammatory papules, with a central facial distribution. However, there is an absence of comedones, nodules, or scarring. See the CKS topic on Rosacea.
• Folliculitis and boils may present with pustular lesions similar to those seen in acne. Swabs usually yield Staphylococcus aureus. Sycosis barbae is persistent folliculitis of the beard area. See the CKS topic on Boils and paronychia.
• Milia are small keratin cysts that may be confused with whiteheads. They tend to be whiter than acne whiteheads, they do not have a central punctum, and they are most commonly found around the eyes.
• Perioral dermatitis presents as erythema and small papules around the mouth, nasolabial folds, and sometimes the lower eyelids. It can have both eczematous and acneiform features, and when acneiform features predominate it may be mistaken for acne. In these cases, the perioral distribution gives the best clue as to its nature.
• Demodex folliculitis is caused by mites and usually occurs in older people. It predominantly affects the face.
• Pityrosporum folliculitis is caused by a yeast-like organism. It tends to affect younger people and predominates on the trunk.

Information on the differential diagnosis of acne vulgaris is from expert opinion described in narrative reviews [Healy and Simpson, 1994; Layton, 2000; Thiboutot, 2000; Wolf, 2002].

• Diagnostic investigations are not necessary for the management of acne vulgaris unless it is suspected as being secondary to an underlying cause in women. Hyperandrogenism should be suspected if the woman has:
• Irregular periods, androgenic alopecia (hair thinning on the front of the scalp), or excessive facial or body hair (hirsutism).
• Acne resistant to conventional treatment (including oral antibiotics), or there is a rapid relapse after a course of oral isotretinoin.
• A sudden onset of severe acne.
• If hyperandrogenism is suspected, consider the following investigations:
• Total and free testosterone — elevated levels may indicate polycystic ovarian syndrome (PCOS) or, rarely, ovarian cancer.
• Luteinizing hormone/follicle-stimulating hormone (LH/FSH) ratio — may be altered in PCOS, with elevated LH.
• Serum dehydroepiandrosterone (DHEA) — elevated levels may indicate adrenal tumour or congenital adrenal hyperplasia.
• 17-hydroxyprogesterone — elevated levels may indicate congenital adrenal hyperplasia.
• Prolactin — may reveal hyperprolactinaemia.
• 24 hour urinary-free cortisol — elevated levels may indicated Cushing's disease or syndrome.

Recommendations for suspecting and investigating hyperandrogenism in women is based on opinion from expert reviews [James, 2005; Ravenscroft, 2005].

• Ask about the problems the person has experienced with their acne. Enquire about:
• The reasons for the person presenting, how long they have had acne, and whether it is worsening.
• Any treatments the person has already tried (for example over-the-counter medication).
• Possible causes or aggravating factors (for example, occupational exposure to halogenated hydrocarbons).
• In women, consider whether the acne could be secondary to a hormonal cause. Features of hyperandrogenism include: irregular periods; androgenic alopecia or hirsutism; acne resistant to conventional treatment (or relapse immediately after a course of oral isotretinoin); and premenstrual flares of acne or a sudden onset of severe acne.
• Assess the severity of the acne. Physically, acne can be categorized as mild, moderate, or severe, but other factors, such as the extent of acne and evidence of scarring, should also be considered.
• Mild acne predominantly consists of non-inflammatory comedones.
• Moderate acne consists of a mixture of non-inflammatory comedones and inflammatory papules and pustules.
• Severe acne is characterized by the presence of nodules and cysts, as well as a preponderance of inflammatory papules and pustules.
• Scarring often indicates previous episodes of severe acne (its presence may warrant more aggressive treatment to prevent further scarring).
• Acne conglobata and acne fulminans are severe variants that require immediate referral.
• Ask about the psychosocial impact of the acne (such as problems at work or school). If the psychological impact seems to be particularly severe or disproportionate, consider using a validated quality of life scale, such as the Cardiff Acne Disability Index (which can be downloaded from www.dermatology.org.uk). This can be used to monitor the person's psychological state during subsequent management.

These recommendations are based on expert opinion from international guidelines [ICSI, 2006; Strauss et al, 2007] and narrative reviews [Webster, 2002; Wolf, 2002; James, 2005; Ravenscroft, 2005; Acne Working Group, 2008].

Categorizing acne severity

• There is no universal grading system for the classification of acne severity [Strauss et al, 2007]. Grading systems have largely been developed for use in clinical trials and rely on lesion counts, but these are generally not suitable for clinical practice [Webster, 2002]. However, there is general consensus from experts that it is useful to categorize acne into three severity grades in order to guide management of the condition.

Psychosocial impact of acne

• During assessment, it is important to recognize the psychosocial impact of acne. It can have a severe negative impact on the person's life. Although often the person tends to overestimate the severity of their acne, the healthcare professional tends to underestimate it. Estimating the physical severity of acne alone is insufficient to guide management, as it may be appropriate to treat acne associated with a greater psychosocial impact more aggressively, or refer the person [Acne Working Group, 2008].