While there is no current direct code for "moisture associated skin damage", there is likely to be in the future. Another term being used by specialists is "Incontinence associated dermatitis". Again there is no direct code for this term at this time.
The code is determined by the location and causative agent. Since you mentioned "diaper rash", it may be that in this case the damage is on the buttocks and/or upper thigh or perineum. Some code options are:
Erythema intertrigo - if the damage is in skin folds - L30.4
Irritation of Perineum - L29.3
Dermatitis due to ammonia (given off by urine and/or stool) - L22
Diaper Dermatitis - L22
Other specified dermatitis - L30.8
Contact Dermatitis due to other (external) agents - L25.8
Other specified disorder of the skin or subcutaneous tissue - L98.8
