Hello ,
Thanks for posting your query.
Itchy rash on face could be most probably an allergy or a drug reaction or less likely infective either fungal or viral infection.
In order to narrow down the possibilities and provide you with specefic advise I would request you to please furnish some details as follows,
1.The onset, duration and progress of the rash.
2.Any past history of allergy or drug reaction in patient or family .
3.Any associated fever, vomiting, respiratory difficulty or diarrhoea.
4.If feasible description of the rash or a photograph which can be uploaded along with your query.
As of now if he has sudden apperance of only rash, no other symptoms its most probably allergic and may subside with anti histaminics like hydroxyzine or cetrizine as per prescribed doses.
Local application of calamine lotion may provide soothing relief.

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