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Bullous pemphigoid is a blistering skin disease that tends to affect the elderly.
It's caused by a problem with the immune system, but usually goes away on its own within a few years. In the meantime, blisters can be controlled with medication.
About 1 in 10,000 people are affected by the condition in the UK each year.
Bullous pemphigoid typically starts with a red, itchy rash that looks a bit like dermatitis (a type of eczema) or hives. This tends to last several weeks or months.
Groups of large, itchy blisters usually then appear on the red patches, just beneath the surface of the skin. They can be up to 5cm in diameter and full of fluid, with the thick skin of the blisters stretched tightly.
The fluid inside is usually clear, but can turn cloudy or bloodstained.
Blisters last a few days before healing without leaving a scar, but a cycle develops where more form.
The rash and blisters are usually seen on the upper arms and thighs, sometimes spreading to body folds and the tummy. In severe cases, the blisters may cover most of the skin, including the inside of the mouth.
However, some people have no symptoms or just have mild redness and irritation without blisters.
The condition is usually seen in older people aged over 70. Rarely, it can affect children and younger adults.
Bullous pemphigoid is also slightly more common in women than men.
Bullous pemphigoid is an autoimmune condition, which means the immune system attacks the body's own tissues and organs.
The person's immune system produces antibodies against the skin. These antibodies attack the basement membrane, which lies between the skin's top layer (epidermis) and the next layer (dermis), and holds the skin together. The skin layers start to separate and fluid builds up in between.
It's not understood why autoimmune diseases like bullous pemphigoid happen, but it's thought something triggers the immune system to attack the body's own tissues. Certain medicines and sunburn have been known to act as a trigger.
Symptoms usually come on unexpectedly.
Bullous pemphigoid isn't:
Your GP may suspect bullous pemphigoid just by looking at your skin.
The diagnosis is then confirmed by taking a small sample of your affected skin (biopsy) and sending it to a laboratory to be inspected to see if the top layers of skin have separated.
Special staining (immunofluorescence) may be used to show up the antibodies, and a blood sample may be taken and checked for the presence of pemphigoid antibodies.
If you've been diagnosed with bullous pemphigoid, you'll probably be referred to a dermatologist (skin specialist) for treatment.
The aim of treatment is to stop new blisters forming and heal the blisters that are already there.
Your specialist may prescribe quite powerful medication with potentially severe side effects, so the smallest possible dose is used to minimise this.
You'll usually be prescribed corticosteroids (either tablets or cream), sometimes alongside "steroid-sparing" medication that allows doctors to reduce the dose of steroids. You may also be prescribed an antibiotic.
Corticosteroids, or steroids, are an anti-inflammatory medicine prescribed for a wide range of conditions.
If the affected area of skin is only small, you may be prescribed steroid cream to rub into the area. For larger areas of blisters, you may be given steroid tablets.
If the blisters are severe, you may be given a high dose to start with to get the condition under control and stop the blisters appearing. This may take several weeks.
The dose is then gradually reduced, and you'll either come off the steroids or be kept on a low dose for a long time.
To use the lowest possible effective dose of steroids, your doctor may give you "steroid-sparing" medicine to take alongside, which is described below.
Read more about steroid medicines, including the side effects.
You may be prescribed azathioprine or methotrexate medicine to take alongside steroids. These work by suppressing your production of antibodies.
The idea is that side effects will be less troublesome if low doses of two different tablets (steroids and immunosuppressants) are used instead of one high dose of steroids. This is known as steroid sparing.
Blisters should be left intact, if possible, to reduce your risk of infection.
However, if they're particularly large and in a difficult place – such as the sole of your foot – they may be carefully pierced with a sterile needle to release the fluid. The skin of the blister should be left.
If blisters do break, they heal quickly.
It's not possible to cure the condition with treatment, but it usually goes away on its own within five to six years. In the meantime, medication is effective in keeping the blisters under control.
Regular follow-up appointments are usually necessary in the meantime so any side effects of the medication can be monitored, and to make sure the symptoms are under control.
If you have bullous pemphigoid, your clinical team will pass information about you on to the National Congenital Anomaly and Rare Diseases Registration Service (NCARDRS).
This helps scientists look for better ways to prevent and treat this condition. You can opt out of the register at any time.