That's because the skin protects the area from infection. If you keep the blister and surrounding area clean and covered, the blister should shrink within a couple of days. Be gentle to the area while it heals. And take steps to keep another blister from forming by wearing shoes that fit properly or wearing an extra pair of socks. Protect your hands with gloves if you are gardening or playing sports.
Few blisters require a doctor's attention.
But if a blister seems extremely swollen, red or painful, contact your health care provider.