you have to find out cause of
rash and if you leave such it will increase leading to severe form with involvement
it can be due to medicines taken for other disease
soaps clothes shampoo oils cooking oils
ointments creams body appliction materials like dyes henna etc
it can be food or clothings you have to corelate and find cause to withdraw the allergen find out by corelating if possible and by tests if you do not come to conclusion
temporarily you can use antiallergics tab and local antiallergic ointments
on the effeted part