Thanks for writing in.
The most common cause in your case scabies
infection or lichen planus
Scabies is caused by a type of ectoparasite called sarcoptes scabies.
It is common and treatable.
You can take oral medications like ivermectin
Also you can apply permethrin lotion overnight.
Keep the area clean and dry.
Lichen planus causes dark colored spots over legs and wrists.It is also treatable with oral and topical steroids
It better to visit a dermatologist
before taking these medication.
I encourage you to visit a qualified dermatologist for proper advise and treatment.
Hope this helps.