Given that this type of rash affects inaccessible and uninviting nooks and crannies of the body, it may be dealt with in a cursory way. In most cases, that won’t be a problem, as the diagnosis may be clear. The differential is wider than many imagine, though, and the symptoms troublesome or painful enough to cause the patient real distress.
- Fungal Infection (Candida or Tinea)
- Seborrheic Dermatitis
- Eczema (e.g. Antecubital and Popliteal Fossae)
- Nappy Rash (Usually a Mixture of Irritant Dermatitis and Candida Superinfection, can Also be Seen in the Incontinent Elderly)
- Irritant Eczema from Sweat
- Flexural Psoriasis
- Staphylococcal Infection (Folliculitis or Impetigo)
- Allergic Eczema (e.g. Deodorant)
- Hidradenitis Suppurativa
- Skin Tags
- Molluscum Contagiosum (Common, but Rarely Presents as Skinfold Rash)
- Acanthosis Nigricans
- Hailey-Hailey Disease
Key distinguishing features of the most common diagnoses
|Fungal Infection||Seborrheic Dermatitis||Erythrasma||Eczema||Nappy Rash|
|Fluoresces Under Wood’s Light||No||No||Yes||No||No|
Possible: Skin scrapings, swab.
Small Print: Investigations to assess for any underlying cause of acanthosis nigricans.
- Skin scrapings: Occasionally needed to confirm a fungal infection if this is in doubt.
- Swabs: Occasionally needed to confirm a suspected staphylococcal infection.
- Investigations to assess for any underlying cause of acanthosis nigricans: This condition is associated with a number of systemic conditions, which might require investigation, depending on the clinical circumstance. This might involve HbA1c or blood sugar for diabetes, LH, FSH, testosterone, SHBG and pelvic ultrasound for PCOS, and hospitalbased investigations if an underlying malignancy (especially gastrointestinal) is suspected.
- As a cause of skinfold rashes, seborrheic dermatitis tends to be symmetrical, and fungal infections less so. That said, they can be difficult to distinguish, and can co-exist, hence the GP ‘catch-all’ prescription of an anti-fungal/steroid cream combination.
- Intertrigo is a loose term with various interpretations – it is most commonly used to describe the seborrheic dermatitis/fungal-type rash described above, but it’s important to remember that ‘intertrigo’ can have other causes.
- When treating fungal groin infections – ‘tinea cruris’ – check for athlete’s foot, too, and treat if present.
- In persistent or troublesome cases, obesity and/or hyperhidrosis may be significant contributory factors – ensure these are addressed, too.
- In resistant cases (even in babies), consider flexural psoriasis. There may be no other evidence of psoriasis evident, and the characteristic scale may be absent – the very well defined lesion edges are a clue.
- Remember that acanthosis nigricans can be associated with underlying malignancy, particularly gastrointestinal. Enquire about relevant symptoms and have a low threshold for referral.
- Patients with ‘recurrent boils’ in groins and/or axillae may well have hidradenitis suppurativa. They are often treated with episodic short courses of antibiotics rather than the more effective long term antibiotics, and the impact of the problem on the individual can be underestimated.
- Always bear in mind the possibility of neglect if you see a baby with horrendous, persistent or recurrent nappy rash, especially if sent by the health visitor rather than spontaneously presented by a parent.