A blister is caused by friction between the skin and the inside of a shoe or clothing. Heat builds up causing a swelling under the skin which may or may not have blood in it.
Prevention is by far the best cure in this case. Most small ones should be left alone and will usually heal on their own, however if you do get one on a long run or walk then there are a few things you can do to ease the pain.
The first sign of a blister will be redness over the skin, possibly at the back of the heel, the instep or toes. This is known as a hot spot and is the early warning sign of a one forming. Applying a second skin dressing, plaster or tape to the affected area can provide an additional protective layer helping to prevent it forming.
Ensure feet are dry and change your socks regularly. Wet socks will cause friction much faster than dry socks. An effective but short term measure is cover the foot and affected area in petroleum jelly. This should provide some relief from pain as it protects the skin and lubricates but as the heat from the foot melts the petroleum jelly it will run away and be ineffective.
Most will drain and heal naturally on their own. For larger blisters it may be necessary to pop them. This should be done with caution, following these guidelines.
Make a small hole at the edge with a sterilized pin or needle. A pin can be sterilized by passing it through a flame. Do not drain a blood filled blister. The skin is protecting the wound from infection. Clean with a sterilising wipe.
Drain the fluid but leave as much of the skin as possible covering the wound. This is an important protective layer for the underlying skin and will help to prevent infection. Cover with a second skin or specialist plaster taking the time to apply it correctly. For additional security apply tape over top.
Preventing it in the first place should be an easy task if you look after your feet and follow are few simple tips.
Shoes - Take care of your footwear. Ensure that shoes fit correctly. Poorly fitting shoes that are either too tight or too big will increase rubbing or friction on the foot and toes. Running shoes should last 6 months or 500 miles. Introduce new shoes gradually and change them before they become too worn out. Look after your walking boots or shoes. Do not leave them on radiators or near heaters. This may cause the leather to shrink and seams protrude.
Taping - Protect the potential hot spots by applying a second skin or taping. Use the highest quality zinc oxide tape which will stay stuck to the foot for longer especially when the feet get wet. A blister plaster is designed specifically to act as a second skin. Make sure they are warm and the foot dry before applying, but once they are on properly they should stay in place for 24 hours and be very effective.
Feet - Keep feet as dry as possible. Wet shoes, boots and socks will cause blisters far quicker than dry ones. Wherever possible change your socks regularly and use foot powder to help keep them dry.
Socks - Some people advocate wearing socks with a double layer. The second layer stops the first one from rubbing against the skin. Others prefer a single layer loop stitched sock as less heat is generated. The important thing is to find what works best for you.
These appear dark or red in color. This is due to damage occurring to blood vessels which bleed into the skin tissues. It tends to occur more from a sudden impact or pinching of the skin, rather than a repetitive friction.
It should be treated in the same way as a normal blister, although be aware that due to the deeper damage, the skin underneath would be raw and usually very sore and more prone to infection.