You have not mentioned about the age of your son.
Usually contact dermatitis
presents with a rash that itches.
Scabies has to be ruled out. If your son has generalized dry skin
, chances are there that winter will cause exacerbation of his itching. In such a case, he might need to keep his skin moist- with good moisturizing lotions like cetaphil
lotion and cetaphil soaps.
In addition he will need anti-histamines like Cetrizine/ Allegra- in right dosage according to his body weight.
If symptoms persist, its better to consult a Dermatologist
Hope my answer helps you.