Your favourite pair of shoes may be off limits for a while if it causes you a blister, but with the right treatment you'll be off the Birkenstocks in no time.
However, what actually is a blister? A 'fluid-filled pocket' says the video, which is quite enough to put you off your food.
But this pocket, while unsightly is actually a good thing - it shows the skin is healing.
Friction blisters tend to occur at point where the skin has been rubbed raw. Don't pop the blister yourself, and if it does so by accident, the NHS advises: "Allow the fluid inside to drain and then cover the blister and the area around it with a dry, sterile dressing to protect it from infection until it heals."
Blood blisters, which is when blood is trapped in with the fluid, need a bit more care.
"Blood blisters are often painful," adds the NHS. "Applying an ice pack to the affected area immediately after the injury can help relieve the pain (a bag of frozen vegetables works just as well). Between 10 and 30 minutes should help."