Full-term infant skin is only between 40% and 60% of the thickness of an adult's skin⁵

Newborn infants seem to have 10 times more hair structures in a given area of skin surface than adults⁶

• Corneocytes and granular cells are smaller in infants than those in adults, suggesting that the turnover of skin cells is more rapid in infant than adult skin⁶

• Skin affected by nappy rash shows greater transepidermal water loss (TEWL) than unaffected areas,⁷ reflecting the compromised barrier function
  

Maintaining an acid pH (between 5 and 5.5 in adults)⁸ is essential for healthy skin function and for the formation of the normal microflora⁴

Skin affected by nappy rash shows higher skin pH than unaffected areas⁷

Using harsh soap and detergents can increase the pH of the skin's outer layers, which could compromise barrier function⁹

Prolonged contact with urine and faeces seems to be the single most important cause of nappy rash¹⁰

Nappy rash typically affects areas exposed to urine and faeces: predominately the buttocks, the perianal area, the genitals, the inner thighs and the waistline¹¹

Prolonged skin wetting - such as from urine - softens and weakens the stratum corneum (maceration)¹⁰

Maceration undermines barrier function, facilitates skin penetration by irritants and increases the child's susceptibility to damage from friction from a nappy^{4,10, 12}

This vulnerability to friction may explain why nappy rash appears to be most common among infants aged between 9 and 12 months of age.  The friction increases as children become increasingly mobile^1,4

Urea in faeces and urine can irritate the child's delicate skin and damage the stratum corneum⁵

Faeces contain proteases, lipases and enzymes that break down protein, fat and urea respectively.  Proteases and lipases can directly undermine skin integrity^1,12

Urase increases skin pH, which enhances the action of proteases and lipases^1,4

A cycle of maceration leading to skin damage, leading to a further undermining of the barrier function and increased susceptibility to the trigger, can become established

Behavioural changes - such as increased crying and agitation, as well as changes in eating and sleeping patterns - may indicate that the nappy rash is causing the child emotional distress¹¹

Parents often report an increase in the frequency of crying and agitation when nappy rash causes an infant discomfort¹¹

Other behavioural indicators of distress, such as eyes squeezed shut and deepening of the nasolabial furrow, seem to be more common in children affected by nappy rash¹¹

Parents may report disrupted eating habits and sleeping patterns as well as less frequent urination and defecation in children affected by nappy rash¹¹

Some infants also show increases in levels of salivary cortisol, a hormone released by the adrenal cortex in response to stress, while they have nappy rash¹¹

Antibiotics and diarrhoea in the previous 24 hours markedly increase the risk of nappy rash¹⁰

Enhanced gastrointestinal transit increases the activity of, and exposure to, proteases and lipases in faeces⁴

Antibiotics commonly cause diarrhoea and can increase the risk of secondary Candida infections¹⁰

Feeding patterns may also influence the risk of developing nappy rash.  Exclusive breast-feeding, for example, seems to reduce nappy rash risk compared to formula feed, perhaps by modulating faecal pH¹

Parents should change nappies immediately after defecation and at intervals throughout the day, depending on the frequency of urination⁴

Changing the nappy at least once during the night seems to reduce the risk of nappy rash⁵

Breast feeding with the child's nappy area exposed avoids occlusion and allows skin to dry^1,5

In the 8 weeks after birth, NICE recommends that parents should not add cleansing agents to a baby's bath water.  When needed, parents can use a mild non-perfumed soap, which is only cleansing agent suggested by NICE¹³

Water does not remove all the oil-soluable contaminants from the skin and is a poor pH-buffer - so daily bathing can compromise maturation of the acid mantle - as well as, in some cases, irritating and drying skin¹⁴

Babies may be bathed 2-3 times a week and the child can be 'topped and tailed' in-between⁵

If nappy rash occurs, a thin layer of barrier ointment helps protect the stratum corneum from over-hydration, irritation from urine and faeces, and friction as well as improving skin hydration, TEWL and pH^4,5,7

Immature skin and occlusion, such as from a nappy, can increase systemic absorption of steroids.  As a result, brief courses of low potency topical steroids are appropriate only when very inflamed dermatitis does not respond to other treatments^1,4

Candida is the most common factor contributing to moderate to severe nappy rash.¹  NICE suggest considering antifungals if painful nappy rash persists¹³

If nappy rash does not respond to topical steroids and, if appropriate, antifungals, the child should be referred to a GP with a special interest in dermatology or a paediatric dermatologist

Nappy rash management increasingly emphasises prevention and protection rather than symptomatic treatment³

Skin protection could be part of each nappy changes and the normal bedtime routine

In response, an international expert panel of dermatologists and paediatricians agreed nine standards for nappy rash preparations (shown right)

The nine standards of an ideal nappy care preparation

The standards stress that any nappy rash preparation should offer proven clinical efficacy and safety in babies³

Used alone, petrolatum jelly is highly occlusive, which can prevent repair of damaged stratum corneum,^3,4 and is not recommended for regular contained use³

Some formulations containing zinc or titanium oxides, which can be difficult to remove and, in turn, cause friction¹⁰

3,10  The expert panel advised against using talcum powder³

Comparison of formulations for a topical nappy rash preparation

The expert panel added that nappy rash preparations should not include components with enhanced allergenicity, antiseptics and preservatives³

Benzyl alcohol, benzyl benzoate and benzyl cinnamate may show enhanced allergenicity

Antiseptics may disrupt the normal skin microflora, potentially increasing the risk of secondary infections

Some studies suggest that parabens, a preservative, may potentially disrupt the endocrine system³

The ideal nappy rash preparation should be pleasant to use, easily applied, and not require removal at each nappy change.  These features are likely to encourage compliance with nappy rash prevention³

Ingredients considered to be unfavorable for a topical nappy rash preparation