Pilonidal disease (pilonidal sinus): symptoms, treatment and recovery

A pilonidal sinus is a small tunnel or pit in the skin, found at the top of the natal cleft, the groove between the buttocks just above the anus. Hospital patient information describes small dents in the skin that develop naturally in this area; a sinus forms in one of these dents, often around a hair follicle. The word pilonidal literally refers to a nest of hair, and hair is usually part of the picture.

Most people with a pilonidal sinus do not notice it at all until it becomes infected. Doctors use the terms pilonidal sinus, pilonidal disease and pilonidal cyst more or less interchangeably, although strictly the problem is a sinus tract rather than a true cyst. The underlying anatomy is not a sign of poor hygiene, and it is not contagious.

The NHS says it is not clear exactly what causes a pilonidal sinus. A skin problem, pressure or friction may push hair between the buttocks inwards. The hair may be growing in the area or may be loose hair shed from the buttocks or elsewhere that gathers in the cleft and then enters the sinus. The Dudley Group NHS Foundation Trust leaflet adds that ingrown hairs, or dents in the skin becoming blocked with hair and skin debris, may play a part, and that pressure or friction may be a factor.

The NHS notes that pilonidal sinuses are more common in men because they tend to be hairier, and that sitting for long periods can increase the chance of developing one. It does not give a precise age range or figures, so any claim about how many people are affected is better left to local clinicians.

When a pilonidal sinus is infected, the NHS describes pain and swelling at the top of the buttock cleft. A pus-filled abscess can develop, sometimes quite suddenly, making it hard to sit down. The area may bleed or leak pus. In some people the infection settles and returns repeatedly, giving ongoing discomfort and regular seeping of pus or blood.

The NHS advises asking for an urgent GP appointment or contacting NHS 111 if you have a small lump at the top of your bottom that is painful, bleeding or leaking pus. These symptoms can develop over a few days, and they are signs of infection that need treating.

• Pain and swelling at the top of the buttock cleft.

• A lump that may feel hot or tender, or that leaks pus or blood.

• Difficulty sitting comfortably.

• Repeated episodes, with discomfort or discharge between flare-ups.

If there is no infection, the NHS says treatment is not needed and a watch-and-wait approach is recommended. It stresses keeping the area between the buttocks clean by showering or bathing regularly, and not shaving the area unless a GP advises it.

A painful, swollen abscess usually needs to be cut open and the pus drained, and antibiotics may be added. The NHS describes this incision and drainage as being arranged on the same day as you see your GP in many cases, under local or general anaesthetic depending on the size of the abscess, usually at hospital with a same-day discharge, and sometimes at the GP surgery. Daily dressing changes follow. Painkillers such as paracetamol and anti-inflammatory medicines are normally offered to ease pain and swelling.

A sinus that is large or repeatedly infected may need an operation. The NHS lists the main choices, and the right one depends on the size of the sinus, how many times it has become infected and the surgeon's experience. The table summarises what the NHS says about each.

NICE has also published guidance on endoscopic ablation for a pilonidal sinus in adults, which it describes as applying heat to the sinus. The guidance was published in April 2019 and is not a leaflet for patients, so ask the surgical team whether it is offered locally.

After surgery you may have a follow-up with your specialist at about six weeks. The NHS advice is to keep the area clean, wear comfortable loose cotton underwear and eat plenty of fibre to avoid straining on the toilet. It also advises avoiding heavy lifting and strenuous exercise for the first week or so, not riding a bike for six to eight weeks, and not swimming until the wound has completely healed.

The Dudley leaflet gives practical hygiene detail for an open wound: wash after each bowel movement and morning and night, use plain water and a soft cloth, avoid soap, rough flannels and talcum powder, dry gently, and change damp dressings for clean dry ones. It lists a swollen, hot or red wound, increasing pain, or a high temperature as signs of infection that need a GP's review.

Most care starts with a GP or an urgent care service, which can arrange drainage of an abscess. Planned surgery is normally delivered by a general or colorectal surgical team as day-case treatment. Which technique is used, and whether newer options such as endoscopic ablation or injection with fibrin glue are available, varies between hospitals. It is reasonable to ask the surgical team why a particular method has been chosen and what the dressing and follow-up arrangements will be.