A pilonidal sinus is a small hole or "tunnel" in the skin. It usually develops in the cleft of the buttocks where the buttocks separate.
More than one hole may develop, and often these are linked by tunnels under the skin.
Most people associate the word sinus with the nose, but sinuses can occur anywhere in the body. Sinus is simply a medical term for a channel or cavity.
A pilonidal sinus will not usually cause any noticeable symptoms unless it becomes infected. This can cause a pus-filled abscess to develop. Signs that you may have an infection include pain, redness and swelling in the affected area.
See your GP as soon as possible if you think you have a pilonidal sinus. Without treatment, any pain and infection may get worse.
Your GP should be able to diagnose a pilonidal sinus after looking at the affected area of skin. Further testing is not usually required.
Why do pilonidal sinuses happen?
The exact cause of a pilonidal sinus is unclear, although it's thought to be caused by loose hair piercing the skin.
Certain things can increase your chances of developing a pilonidal sinus, such as being obese, having a large amount of body hair, and having a job that involves a lot of sitting or driving.
How are pilonidal sinuses treated?
If you have a pilonidal sinus, it's important to keep the area clean and dry. It may also help to remove any hair near the sinus. These steps can reduce the risk of infection.
Showering at the end of the day to remove stray hairs from the cleft between your buttocks may also help.
If a pilonidal sinus becomes infected, it should be treated as soon as possible, as it's likely to get worse.
Treatment usually involves taking antibiotics and having the pus drained from the abscess during a minor operation called incision and drainage.
If the sinus keeps becoming infected, it may have to be surgically removed. Several techniques can be used, including:
cutting out the sinus and leaving the wound open so it can heal, and packing it with a dressing daily
closing the wound with a flap of skin and stitches
scraping out the sinuses and filling them with a special glue
Who is affected?
Pilonidal sinuses are rare, affecting about 26 in 100,000 people each year.
They affect at least twice as many men as women. The average age for a pilonidal sinus is 21 in men and 19 in women.
They are less common in children and people over the age of 45.
Pilonidal sinuses commonly occur at the top of the buttocks
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Symptoms of a pilonidal sinus
A pilonidal sinus is a small hole or channel in the skin that usually occurs at the top of the cleft between your buttocks.
It may not cause any noticeable symptoms unless it becomes infected.
Pilonidal sinuses have also been known to develop on the belly button or between fingers. In many cases, there is more than one channel.
If the sinus becomes infected, an abscess will usually develop. An abscess is a painful collection of pus that causes symptoms such as:
a tender lump under the skin
redness of the skin
pus draining from the sinus – the pus usually smells unpleasant
blood draining from the sinus
a high temperature of 38C (100.4F) or above, although this is uncommon
These symptoms may develop quickly, often over a few days.
The pain caused by a pilonidal sinus can be severe and is likely to get worse without treatment. This can make it difficult to sit or lie down comfortably, which may affect your sleep. The pain may also affect your ability to work and your daily activities.
See your GP as soon as possible if you suspect you have the condition. They can examine you and discuss possible treatments.
Causes of a pilonidal sinus
The exact cause of pilonidal sinuses is unclear. It is generally thought they are caused by loose hairs pushing into the skin.
They could also be caused by deep layers of skin being stretched and moved, leading to a hair follicle rupturing.
Hair follicles are the small holes that an individual hair grows out of. Pressure and friction on a hair follicle could somehow damage it, causing a pilonidal sinus.
If a hair follicle becomes blocked, it can become enlarged and then burst. A broken hair may push into the skin, leading to an infection.
This may explain why pilonidal sinuses are common around the buttocks, as sitting and driving will cause pressure and friction in this area.
There have been reports of hairdressers developing pilonidal sinuses on their hands. This may be caused by hair becoming trapped in moist, damaged skin between a hairdresser's fingers.
Infection of the pilonidal sinus
If a broken hair pushes into the skin, the skin becomes irritated, red and swollen. Bacteria can quickly infect this skin. The cleft between the buttocks is an ideal place for bacteria to spread, as it is often moist and warm.
When the skin is infected, the immune system (the body's natural defence against infection and illness) tries to fight the bacteria, which results in a collection of pus known as an abscess.
Some things are known to increase your risk of pilonidal sinuses, including:
obesity – having a body mass index (BMI) of 30 or above
age – pilonidal sinuses can occur at any age, but are more common in young adults between the ages of 15 and 40
having an above-average amount of body hair, which may be why more men are affected than women
having coarse and curly body hair
a previous injury to the affected area of skin – for example, from a fall
having a deep cleft between your buttocks
having a family history of the condition – more than one-third of people have a family member with the condition
having a job involving a lot of driving or sitting down for long periods
During the Second World War, thousands of army jeep drivers developed pilonidal sinuses. The condition became so widespread it was nicknamed "jeep seat", or "jeep disease".
As so many men doing the same sort of job developed the condition, this suggests environmental factors must play a role in its development. These factors could include:
wearing restrictive clothing – such as army uniforms
repetitive motion – such as bouncing around in the seat of a jeep
poor personal hygiene
Treating a pilonidal sinus
Treatment may not be necessary for a pilonidal sinus if it's not infected.
It's important to keep the area as clean and dry as possible. Removing hair from the area is also advisable, usually by shaving or using hair removal creams. This should reduce the risk of an infection.
If your pilonidal sinus does become infected, surgery is likely to be recommended.
Incision and drainage
Incision and drainage involves opening the sinus up and draining away the pus. This procedure can usually be carried out at your local hospital under general anaesthetic, so you will be asleep during the operation.
It's a relatively minor operation, so you should be able to return home either the same day or the day after the procedure.
After the operation, a dressing is applied to help the wound heal. It should be arranged for your dressing to be changed daily by the practice nurse at your local GP surgery.
Many sinuses are cured after incision and drainage.
Treating recurring infection
When there is discharge of pus from the sinus without an abscess present, antibiotics may be prescribed to keep the infection under control while you wait to see a surgeon. However, this will not cure the pilonidal sinus.
If the pilonidal sinus keeps becoming infected, surgery may be recommended to remove the sinus and prevent further infections. This can be done in a number of ways. In most cases, operations called wide excision or excision and primary closure are used.
The treatment method should be decided jointly with your surgeon after you have discussed the options.
During wide excision, the surgeon cuts out the section of skin containing the sinus. The wound is left open and packed with a dressing.
The advantage of having a wide excision is that the chances of an infection returning are low. But the wound will take a long time to heal and your dressings need to be changed daily for two or three months.
Recent evidence suggests less invasive procedures, such as off-midline primary closure or sinusotomy, may now be preferred.
Excision and primary closure
During an excision and primary closure, the surgeon cuts out the section of affected skin before closing and sealing the wound with stitches. The advantage of this technique is that the wound heals quickly. However, the chances of the infection returning are higher than with a wide excision.
There are different methods of using a flap of your own skin and tissue to fill and close the wound. Your surgeon can explain the technique they will use in more detail, but techniques where the wound is closed off the midline have found to be better.
Some pilonidal sinuses can be treated by scraping away ingrown hairs and other debris from the sinus before sealing the area with a special absorbable glue called fibrin glue. This can be done under general orlocal anaesthetic, depending on your preference.
The advantage of this treatment is you don't need any dressings and there is little pain. You will probably be able to return to normal activities within a week. The risk of infection is similar to excision and primary closure. However, this procedure is relatively new and may not be available in your local area.
You may feel some discomfort after your operation. You should be given pain relief, and you may also be given painkillers to take at home. You will usually be discharged on the day of your operation.
After your operation, you will probably need time off work, although this depends on how you are feeling and the type of work you do. Avoid strenuous work for up to two weeks.
You can start to exercise and play sport as soon as you feel able to. However, if you have stitches, you may need to avoid activities that could disrupt the stitches for two to four weeks.
Whatever type of operation you have, it is important to keep the site of the wound clean. Your surgeon can offer advice on how to do this, which may include the following:
Have a shower or bath at least once a day if your wound is being left open and packed with a dressing.
If your wound is closed with stitches, avoid having a bath. You may be advised to keep the wound completely dry for the first few days. Ask your surgeon for advice.
When washing the wound, do not use soap because this will irritate your skin. Use plain water and a soft cloth instead.
Do not use talcum powder.
Carefully dry the area after washing using a soft towel, but do not rub the skin. Using a hair dryer is a good way of drying the area.
Always remove a damp or wet dressing and replace it with a dry clean one.
Wear loose-fitting cotton underwear and avoid synthetic underwear, such as nylon.
Eat high-fibre foods to help soften your stools and reduce any straining when you go to the toilet.
Several complications can occur as a result of surgery for a pilonidal sinus. These include:
a pilonidal sinus returning after treatment (recurrent pilonidal sinus)
infection at the site of the wound during or after surgery
Contact your GP immediately if you notice any signs of infection, such as:
red, swollen skin
a high temperature of 38C (100.4F) or above
a feeling of heat at the site of the wound
fluid, pus or blood leaking from the site of the wound
an unpleasant smell coming from the site of the woun