I agree with Gerry. I'd also add that if he's wearing long socks (presumably also dried with the dryer sheets), that might not be helping matters.
Years ago, I requested information from the federal government (forget the department name...Consumer Product Safety Commission?) on complaints filed regarding scented laundry detergent and dryer sheets. There were many complaints noting itchy skin, asthma, etc.
The reason I investigated this is due to a neighbor's dryer venting out nearby our bedroom windows. My husband and I would get headaches when she was running laundry from the fragrance fumes.
I offered a box of unscented detergent and fabric softener to her, asking if she'd mind trying please. She did, and later reported that the hives that she and her daughter had long suffered from went completely away.
Some research indicates that these laundry products contain toxic compounds:
http://www.scienceblog.com/cms/toxic-chemicals-found-common-scented-laundry-products-air-fresheners-16960.html
My understanding is that the fragrance industry is essentially accountable to no one as far as safety. Some won't even divulge ingredients, citing competitive reasons.