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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.
Read more about the symptoms of pilonidal sinus.
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.
Read more about the causes of pilonidal sinus.
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:
Read more about treating pilonidal sinus.
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.
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:
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.
Read more about treating 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.
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:
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:
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 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.
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.
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 or local 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:
Several complications can occur as a result of surgery for a pilonidal sinus. These include:
Contact your GP immediately if you notice any signs of infection, such as: