From the symptoms contact dermatitis, sweat dermatitis, hives and heat rash need to be ruled out. The other possibility is of lichen planus. Lichen planus is an inflammatory disease that affects the skin and the oral mucosa, and presents itself in the form of papules(flat spots) or rashes. It is an itchy papular eruption characterized by its violaceous color
Treatment is available only on prescription and consists mainly of steroids, retinoids, hydroquinone and phototherapy.
I hope it helps. Take care and regards.