Allergy does cause an itchy swollen rash... often without fever and at times may progress to respiratory discomfort.. and hence need to be promptly understood treated and prevented. Common allergies are related to diet protein nut/egg/oats/milk/fish etc
Around winter.. three types of viral rashes are often seen. Although any viral fever including dengue fever can rash; the viral rash is often strongly described and seen with measles and chicken pox and hand foot mouth disease.
Commonest of these 3 being hand foot mouth disease HFMD... is the mildest of all and often may not need any specific measures unless has bad oral sores or complications. Its easy to know that HFMD rash is small reddish mini fluid bumps and doesnt affect trunk or back and often has a mouth sore. Fever may be short and mild. All may disappear in two weeks though can spread very fast.
Chicken pox on other hand…