According to How Stuff Works, up to one pint of sweat is produced by both feet in one day. Each foot contains more than 250,000 sweat glands. Excessive sweating is called hyperhidrosis.
The body uses sweat to cool off, and normally the fluid produced quickly evaporates. However, when sweat is excessive, and is trapped in the glands, bacteria grows because of its strong attraction to the sweat composition of salt and water. When bacteria "feeds" on sweat, it gives off a strong smell as it eliminates waste products. According to Foot Vitals, sweaty feet contribute to athlete's foot, plantar warts, itching and toenail fungus.