• Diagnose nappy rash from the characteristic appearance of the rash and by excluding other diagnoses of rash in the nappy area (especially in neonates, as nappy rash is uncommon in this age group).
• Typically there is redness over convex surfaces closest to the nappy (buttocks, genitals, pubic area, and upper thighs) with sparing (no redness) in the deeper flexures.
• The rash has a glazed appearance if acute, or fine scaling if more long-standing.
• Usually, there are no symptoms (scratching or systemic upset). However, if the nappy rash is severe or painful, the child may be distressed or uncomfortable.
• A skin swab is not necessary to make a diagnosis.

Clinical features

• Expert opinion from review articles indicates that nappy rash can be clinically distinguished from other rashes (such as eczema) in the nappy area [Gupta and Skinner, 2004; Scheinfeld, 2005].

Excluding other causes

• It is important to exclude other causes of rashes in the nappy area. For example, perianal streptococcal dermatitis is often misdiagnosed as nappy rash, and will remain unresponsive to standard treatment; however, it will resolve rapidly with antibiotic treatment [Brilliant, 2000].

• Primary bacterial infections
• Impetigo:
• Is an infection of the superficial layers of the skin, usually caused by Staphylococcus aureus, and less commonly by Streptococcus pyogenes.
• Typically, thin-walled vesicles or pustules are present which rupture; the overlying exudate dries to form thick, yellow–brown or golden crusts.
• For more information, see the CKS topic on Impetigo.
• Perianal streptococcal dermatitis:
• Presents as a bright red, sharply demarcated rash that is commonly misdiagnosed and treated as a fungal infection.
• It occurs most commonly in children 3–4 years of age. It remains unresponsive to treatment with topical steroids and antifungal creams.
• Perianal pain and itching are common and blood-streaked stools occur in up to a third of cases.
• Infantile seborrhoeic dermatitis
• Seborrhoeic dermatitis usually affects the scalp, ears, eyebrows, neck, and axillae, but may also affect the nappy area.
• It presents as well-defined areas of redness and scaling, which do not seem to disturb the child.
• It most commonly starts between the second week and sixth month of life; it usually clears within a few weeks and does not recur.
• For more information, see the CKS topic on Seborrhoeic dermatitis.
• Atopic eczema
• An increased tendency to develop nappy rash may be the initial presentation of atopic eczema (often the nappy area is spared as this area is so well hydrated and not accessible to excoriation).
• A tendency to dry skin, a positive family history of atopic eczema, and rash affecting other skin areas help to distinguish it from a primary nappy rash.
• For more information, see the CKS topic on Eczema - atopic.
• Eczema herpeticum
• Disseminated herpes simplex virus infection (eczema herpeticum) presents with widespread lesions that may coalesce into large, denuded, bleeding areas that can extend over the entire body.
• For more information, see the CKS topic on Eczema - atopic.
• Psoriasis
• Infantile psoriasis is uncommon, and when it occurs it most typically affects the nappy area.
• The rash may have a well-demarcated edge and characteristic adherent scales, although in the nappy area this typical appearance is usually significantly modified by occlusion and friction.
• Psoriasis starts in the second month of life and generally lasts 2–4 months before resolving. Affected infants have a greater chance of developing psoriasis in adulthood.
• Allergic contact dermatitis
• Other types of contact dermatitis are uncommon causes of nappy rash.
• They are distinguished by their characteristic patterns of distribution following exposure to potential irritants or allergens such as nappy dyes, detergents, drug reactions (such as antibiotics), and baby wipes with perfumes and fragrances added.
• For more information, see the CKS topic on Dermatitis - contact.
• Rare causes of nappy rash
• Zinc deficiency may present with nappy rash that fails to respond to normal treatments. It is more common in premature infants and is associated with dermatitis around the mouth and erosive lesions of the nails and palmar creases.
• Langerhans' cell histiocytosis commonly presents in the third month of life with persistent intertrigo. Initially small, yellow papules develop which become confluent and subsequently ulcerate.