According to the symptoms you described, an inflammation of the foreskin has occurred. The inflammation can be due to friction (like in regular skin blisters when wearing new shoes). An allergic reaction to a substance might have caused this, too. In the end, if he has allergies to other substances present at the moment, the level of histamine in the body might be increased. The friction on parts of the body that are formed from a tissue that is more loose (the foreskin, eyelids) can make them swell. You might want to see a dermatologist to see if the reaction was due to a kind of allergy and determine the exact allergen.