Irritant diaper dermatitis (IDD, also called a diaper/nappy rash) is a generic term applied to skin rash in the diaper nappy area that are caused by various skin disorders and/or irritants. Generic irritant diaper/nappy  dermatitis is characterized by joined patches of erythema and scaling mainly seen on the convex surfaces, with the skin folds spared. Diaper/nappy dermatitis with secondary bacterial or fungal involvement tends to spread to concave surfaces (i.e. skin folds), as well as convex surfaces, and often exhibits a central red, beefy erythema with satellite pustules around the border. It is usually considered a form of irritant contact dermatitis. The word "diaper" is in the name not because the diaper/nappy itself causes the rash but rather because the rash is associated with diaper use, being caused by the materials trapped by the diaper (usually feces). Allergic contact dermatitis has also been suggested, but there is little evidence for this cause. In adults with incontinence (fecal, urinary, or both), the rash is sometimes called incontinence-associated dermatitis (IAD).The term diaper candidiasis is used when a fungal origin is identified. The distinction is critical because the treatment (antifungals) is completely different. Causes
Irritant diaper dermatitis develops when skin is exposed to prolonged wetness, increased skin pH caused by the combination, and subsequent reactions, of urine and feces, and resulting breakdown of the stratum corneum, or outermost layer of the skin. This may be due to diarrhea, frequent stools, tight diapers, overexposure to ammonia, or allergic reactions.
Atopic dermatitis, or eczema, is associated with allergic reaction, often hereditary. This class of rashes may appear anywhere on the body and is characterized by intense itchiness. Treatments
Possible treatments include minimizing diaper use, barrier creams, mild topical cortisones, and antifungal agents. A variety of other inflammatory and infectious processes can occur in the diaper area and an awareness of these secondary types of diaper dermatitis aids in the accurate diagnosis and treatment of patients.Overall, there is sparse evidence of sufficient quality to be certain of the effectiveness of the various treatments. Washcloths with cleansing, moisturising and protective properties may be better than soap and water, and skin cleansers may also be better than soap and water, but the certainty of evidence with regard other treatments is very low. Diaper changing
The most effective treatment, although not the most practical one, is to discontinue use of diapers, allowing the affected skin to air out. Another option is simply to increase the frequency of diaper changing. Thorough drying of the skin before diapering is a good preventive measure because it is the excess moisture, either from urine and feces or from sweating, that sets the conditions for a diaper rash to occur. Diaper type
Some sources claim that diaper rash is more common with cloth diapers. Others claim the material of the diaper is relevant insofar as it can wick and keep moisture away from the babys skin, and preventing secondary Candida infection.