 [ Symptoms ] does synthetic underwear cause jock itch  all the running and exercise people say to avoid cotton since it gets wet and causes irritation however jock itch prevention says to go with cotton undies which is it to cotton or not to cotton [ Disease ] you did not mention if his foot was swollen and or has any red lines in the area it could be as simple thing as gout which is very painful and common for his age he would need further test to find the root of the problem