Why do my hands swell up after exercising \?

Just your hands? There is a condition called physical or cholinergic urticaria--hives resulting from physical activities, but often else where on body as well, not just hands. They can be quite swollen (as piture here) and at times quite itchy. Exercising in cooler weather lessens it a bit. Swimming is less likely to cause hives in such case. If it is bothering you, consult doc for eval. Good luck.