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What is a blister?

A blister is a fluid pocket in the skin which develops when the upper skin layers separate and the space between them fills with serum. Serum is the liquid part of the blood - it contains protective substances like antibodies.

The appearance is of a bubble on the skin. Sometimes a small blood vessel will bleed into the bubble (blood blister) in which case, rather than being clear, it will be red. Occasionally the contents of a blister will become infected and the the blister may then contain pus.

Most blister formation is a self-defence strategy by the body. The purpose is to protect the skin beneath from further injury and to encourage fast healing. The associated pain also has a protective effect. Blisters result from pressure and friction and the activity causing them is less likely to continue if they become increasingly painful.

What causes blisters on feet?

Blisters are most common on the feet and ankles as these are the areas most subject to pressure in most people.

Generally blisters may be caused by:

• Friction - the most common cause in the feet.

• Direct damage to the skin by corrosive substances or heat.

• Some infectious diseases (for example, Windpocken).

• Some inherited diseases (for example, pompholyx).

• Allergic reaction.

This leaflet focuses on foot blisters caused by friction. Areas of the foot will suffer repeated friction where there are:

• Poorly fitting or rigid shoes which rub on walking.

• High heels (which force pressure on to a small area of the foot, often the ball of the foot).

• Hot or moist feet which result in the skin being more vulnerable.

• Ill fitting socks or socks with wrinkles.

• Shoes being worn without socks.

• Abnormalities of foot shape which can affect shoe fit.

Additionally blisters on feet will be more likely to form if someone:

• Is walking or running for a long time, particularly with any of the factors above.

• Is walking or running in uncomfortable shoes whilst carrying weight (for example, shopping or luggage).

• Has a condition causing reduced sensation in the feet (for example, Diabetes oder periphere Neuropathie). If theycan't feel pain in the feet, they are more likely to carry on without realising when something is rubbing.

Should you pop a blister?

The general rule with blisters is do not pop or drain them. Popping the blister makes a hole in the skin (which wasn't there before). This not only removes the protective effect of the blister but opens the area up to infection. Popped blisters are often more painful too as the nerves in the skin beneath are more exposed.

It is particularly important to try to keep the blister intact if any of the following apply, as these conditions make people more prone to infection and worsening damage to feet:

• Diabetes.

• Herzinsuffizienz.

• Periphere arterielle Verschlusskrankheit.

• Geschwollene Beine mit venöse Geschwüre.

• Conditions reducing your immunity, wie zum Beispiel HIV.

• People taking steroid tablets.

As with every rule there are exceptions. A blister may need to be popped if it is large and affecting the ability to wear shoes. It may be better to pop it if it is so tense that it is likely to pop by itself on wearing shoes. A controlled de-pressurisation of the blister may then make a smaller hole in the skin than if shoes rubbed the dome of the blister off completely.

How to treat blisters on feet

Most blisters will heal by themselves and the blister fluid will be gradually re-absorbed as the skin beneath heals. This healing can be sped up by:

• Removing the cause - wearing different shoes and spending time barefoot if possible.

• Keeping the area clean and dry.

• Wearing well-fitting socks with shoes.

• If the blister is small - up to the size of a pea - a protective dressing will stop it breaking. The top layer of the blister then protects the skin beneath whilst it heals.

• If the blister is on the underside of the foot it is helpful to make a protective blister dressing using a moleskin pad with a hole cut in the middle like a doughnut. This takes the pressure off the blister and prevents the top from rubbing off.

• Commercial blister plasters can be very helpful and come in a number of sizes and shapes. These should be applied according to the instructions. They should not be removed until they drop off (this can take a week or longer), as they function as a 'second skin' until the blister has healed. An added advantage of this method for those on walking trips is that they can then continue their journey without doing further damage.

If the blister is large and tense and will clearly burst on its own, it may be advisable to pop it (but with the cautions above).

In this case the principle of draining the blister is to make as small a hole as possible in a sterile manner. The top of the blister should ideally be preserved to act as protection for the skin beneath. This can be done by:

• Washing hands with warm water and antibacterial soap.

• Sterilising a needle or pin - for example, in a flame and then letting it cool or by wiping it with an alcohol wipe.

• Gently puncturing the blister towards the edge.

• Gently letting or squeezing the fluid out - the dome will collapse and sit on the skin beneath.

• Applying an antiseptic cream (such as Savlon®) if possible,

• Applying a clean dressing and changing it if it gets wet or dirty.

• Avoiding getting the area wet for at least 24 hours. This will allow the skin from the top of the blister to have a chance to 'fuse' on to the skin beneath.

If a blister has already burst, it should be:

• Washed with soap and water.

• Dealt with as follows: the skin flap should be smoothed down if possible,unless it's very dirty or there is pus under it, in which case it won't stick and may be better removed.

• Covered with a dressing (and antiseptic cream applied if possible).

• Treat as above.

When your blister is healing it should be monitored for signs of infection which might include:

• Increasing pain.

• Increasing or spreading redness.

• Pus on or around the blister.

• Swelling and heat.

• Eine hohe Temperatur (Fieber).

Complications of foot blisters

Most friction blisters heal naturally and quickly. Possible complications include:

• Infection, which could spread. See the separate leaflet called Wound Infection.

• Ulcer formation (particularly likely if sensation or circulation is poor, as in diabetes, peripheral arterial disease and neuropathy). See the separate leaflet called Diabetes, Foot Care and Foot Ulcers.

How to prevent blisters on feet

Blisters on feet can be prevented by reducing the friction that causes them. This can be helped by:

• Wearing comfortable, well-fitting shoes and clean socks.

• 'Breaking in' new shoes, including running or walking shoes, gradually.

• Sensible shoe choice. Shoes such as high heels and dress shoes are more likely to lead to blistering, so wear these for shorter periods.

• Stopping activity as soon as possible if a pressure point starts to rub, and removing/changing shoes.

• Wearing moisture-wicking socks, or changing socks frequently which helps prevent moisture build-up if you tend to get sweaty feet. Sports socks can help keep feet drier.

• Ensuring that shoes or hiking boots have been properly broken in before a long walk.

• Taping a protective layer of padding between the affected area and the footwear if shoes are rubbing when out and about and can't be removed. This can prevent the formation of a blister. A friction-management patch applied to the shoe will remain in place much longer. This can be helpful with speciality shoes and boots like ice skates and inline skates, and with orthotic braces and splints.

• Putting a lubricant like talcum powder inside the shoes may also reduce friction in the short term. However, because the talc absorbs moisture, it can make things worse in the long term.