Viral exanthem https://en.wikipedia.org/wiki/Exanthem
Viral exanthem is a widespread rash that appears on the surface of the skin, most commonly in children. An exanthem can be caused by toxins, drugs, microorganisms, or autoimmune disease. Many common viruses can produce a rash as part of their symptoms. Varicella zoster virus (chickenpox or shingles) and mumps should be considered when selecting treatment.

Treatment ― OTC Drugs
OTC antihistamines may help relieve rashes and itching.
#Cetirizine [Zytec]
#Diphenhydramine [Benadryl]
#LevoCetirizine [Xyzal]
#Fexofenadine [Allegra]
#Loratadine [Claritin]
More information ― English
References Viral exanthems 12952751
Eruptive pseudoangiomatosis, Erythema infectiosum and parvovirus B19, Gianotti-Crosti syndrome (papular acrodermatitis of childhood), Hand-foot-mouth disease, Herpangina, Measles (rubeola), Papular-purpuric gloves and socks syndrome, Pityriasis rosea, Roseola infantum (exanthem subitum), Rubella (German or 3-day measles), Unilateral laterothoracic exanthem (asymmetric periflexural exanthem of childhood)