A blister is a pocket of fluid which forms a bubble in the upper layers of the skin. Blisters on the feet are normally caused by a mixture of friction and pressure. They can be very painful. The word "blister" comes from the Old French "blostre" which meant a nodule caused by leprosy.
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, in which case rather than being clear it will be red. Occasionally the contents of a blister will become infected and the contents will become cloudy as 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 encourage fast healing. The associated pain also has a protective effect. Blisters are caused by pressure and friction and we are therefore less likely to continue the activity that causes them if they become increasingly painful.
What causes foot blisters?
Blisters are most common on the feet and ankles, as these are the areas most subject to heat and 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, chickenpox).
- Some inherited diseases (for example, pompholyx).
This article focuses on foot blisters caused by friction. Areas of the foot will suffer repeated friction if you:
- Have poorly fitting or rigid shoes which rub as you walk.
- Wear high heels (which force pressure on to a small area of the foot, often the ball of the foot).
- Have hot or moist feet (this reduces skin integrity).
- Have wrinkles in your socks.
- Wear shoes with no socks.
- Have abnormalities of foot shape, affecting shoe fit.
Additionally blisters will be more likely to form on your feet if you:
- Walk or run for a long time, particularly with any of the factors above.
- Walk or run in uncomfortable shoes whilst carrying weight (for example, shopping or luggage).
- Have a condition causing reduced sensation in your feet (for example, diabetes or peripheral neuropathy).
Should I pop a blister?
The general rule with blisters is do not pop or drain them. If you pop the blister, you have made 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 to you, as you will be more prone to infection and worsening damage to your feet:
- Heart failure.
- Peripheral arterial disease.
- Swollen legs with venous ulcers.
- Conditions reducing your immunity, such as HIV.
- You are taking steroid tablets.
As with every rule, there are exceptions. You may need to pop a blister if it is large and getting in the way of your shoes. You may also judge that it's better to pop it as it is so fluid-filled and tense it's likely to pop anyway as soon as you put your shoes back on. A controlled de-pressurisation of the blister may then make a smaller hole in the skin than if your shoes rubbed the dome of the blister right off.
How do I treat a foot blister?
Most blisters will heal by themselves and the blister fluid will be gradually re-absorbed as the skin beneath heals. You can speed this up and decrease pain by home treatments:
- Remove the cause - wear different shoes and spend time barefoot if you can.
- Keep the area clean and dry.
- Wear 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 your 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. Apply one of these according to the instructions. You should not remove it until it drops off, as it functions 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 if you don't let the fluid out, you may decide 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 you can in as sterile a way as possible. Aim to preserve the top of the blister to act as protection for the skin beneath. You do this by:
- Sterilising a needle or pin - for example, in a flame, by wiping it with an alcohol wipe or (if you have nothing else) by putting it in boiling salted water for ten minutes.
- Gently puncturing the blister towards the edge.
- Gently expressing the fluid - the dome will collapse and sit on the skin beneath.
- Applying an antibiotic ointment if you have any, and a clean bandage.
- Changing the bandage 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 you have a blister which has already burst:
- Wash with soap and water.
- Smooth the skin flap down if you can. Do this unless it's very dirty or there is pus under it, in which case it won't stick and may be better removed.
- Apply antibiotic ointment and a bandage.
- Treat as above.
When your blister is healing keep an eye on it for signs of infection which might include:
- Increasing pain.
- Increasing or spreading redness.
- Pus on or around the blister.
- Swelling and heat.
- A high temperature (fever).
What are the complications of foot blisters?
Most blisters heal naturally and quickly. Possible complications include:
- Infection, which could spread.
- Ulcer formation (particularly likely if sensation or circulation is poor, as in diabetes, peripheral arterial disease and neuropathy).
How do I prevent foot blisters?
Blisters 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 shoes - gradually.
- Stiffer shoes. Shoes such as high heels and dress shoes are more likely to lead to blistering, so wear these for shorter periods.
- Socks that manage moisture, or frequent sock changes which help 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 you are out and about and can't take them off. 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 can also reduce friction in the short term. However, because the talc absorbs moisture, it can make things worse in the long term.
Dr Mary Lowth
Dr Mary Lowth
Dr Hayley Willacy