Behçet's disease can cause a wide range of symptoms, but it is rare for someone with the condition to have all of them at once.

In most cases, there will be times when the symptoms improve (remission) and times when they get worse (flare-ups or relapses).

The main symptoms of Behçet's disease are outlined below.

Mouth ulcers

Almost everyone with Behçet's disease will develop mouth ulcers. The ulcers look the same as normal mouth ulcers, but can be more numerous and painful. They most often develop on the tongue, lips, gums and the insides of the cheeks.

The ulcers usually heal within a couple of weeks without leaving any scarring, although they will often return.

Genital ulcers

Like mouth ulcers, recurrent genital ulcers are also a common symptom of Behçet's disease.

In men, the ulcers usually appear on the scrotum. In women, they usually appear on the cervix (neck of the womb), vulva or vagina. However, genital ulcers can appear anywhere in the groin area, including on the penis.

The genital ulcers are usually painful and leave scarring in around half of all cases. Men may also experience inflammation (swelling) of the testicles and women may find the ulcers make having sex painful.

Genital ulcers caused by Behçet's disease are not contagious and cannot be spread through sexual intercourse.

Skin lesions

Many people with Behçet's disease will also develop skin lesions. A lesion is any type of unusual growth or abnormality that develops on your skin, such as a bump or a discoloured area of skin.

Skin lesions that can occur in Behçet's disease include red, tender swellings on the legs called erythema nodosum and more widespread acne-like spots called pseudofolliculitis.

Skin lesions will often heal within 14 days, although they may come back frequently. Erythema nodosum lesions may leave permanently discoloured areas of skin.

Inflammation of the joints

Behçet's disease affects the joints in up to two in every three people with the condition, causing arthritis-like symptoms such as pain, stiffness, swelling, warmth and tenderness.

The joints most often affected include the knees, ankles, wrists and small joints in the hands.

Unlike some conditions affecting the joints, permanent joint damage is rare in Behçet's disease and symptoms can usually be controlled successfully.

Inflammation of the eyes

Inflammation of the eyes is another common symptom of Behçet's disease, occurring in around half of all cases. It often develops very suddenly.

Inflammation often affects the uveal tract, which is a group of connected structures inside the eye. Sometimes both eyes may be affected at the same time.

Inflammation of the uveal tract is known as uveitis and it can cause symptoms that include:

• painful red eyes
• floaters (dots that move across the field of vision)
• blurred vision

In the most severe cases of Behçet's disease, inflammation of the eyes can lead to permanent visual impairment. However, this is far less likely with early and appropriate treatment.

Sensitive skin

In some people with Behçet's disease, the skin is particularly sensitive to injury or irritation. This is known as pathergy.

For example, if a needle is used to prick the skin of someone who has pathergy, a large red bump would develop within a day or two that appears out of proportion to the original needle prick.

Gastrointestinal symptoms

Behçet's disease can cause inflammation of the stomach and bowel, which can lead to symptoms such as:

• feeling sick and vomiting
• abdominal (tummy) pain
• indigestion
• loss of appetite
• diarrhoea

Occasionally, the inflammation can cause the bowel to become damaged and bleed. Having blood in your stools is a possible symptom of inflammation of the internal lining of the bowel.

Blood clots

The inflammation of the lining of the blood vessels associated with Behçet's disease can sometimes cause blood clots to form. The medical term for blood clots is thrombosis.

Deep vein thrombosis

One of the most common types of blood clot to affect people with Behçet's disease is deep vein thrombosis (DVT). 

This is where a blood clot develops in one of the deep veins of the body, usually in the legs. Symptoms include:

• pain, swelling and tenderness in one of your legs (usually in the calf)
• a heavy ache in the affected area
• warm skin in the area of the clot
• redness of your skin, particularly at the back of your leg below the knee

DVT often requires immediate medical treatment. If you suspect that you or someone in your care has the condition, you (or they) should go to your nearest accident and emergency (A&E) department immediately.

In people with Behçet's disease, careful assessment will be needed to determine if it is safe to use blood thinning treatment for this complication.

Cerebral venous thrombosis

A less common type of blood clot associated with Behçet's disease is cerebral venous thrombosis (CVT). This occurs when a blood clot develops inside the blood vessels that run through channels located between the outer and inner layer of your brain.

The blood clot can increase the pressure inside your skull and also lead to an interruption of the blood supply to the brain (stroke).

Symptoms of a CVT include:

• a severe headache – this has been described as throbbing, piercing, a band of pain, or as a very severe pain that suddenly appears out of nowhere
• slurred speech
• seizures (fits)
• hearing loss
• double vision
• stroke-like symptoms, such as muscle weakness or paralysis – but, unlike most strokes, both sides of the body can be affected

CVT should be regarded as a medical emergency. If you suspect that you or someone you know is experiencing a stroke, you should dial 999 immediately to request an ambulance.

Aneurysms

Inflammation of the blood vessels can cause part of your blood vessels' walls to weaken. This causes the walls to bulge outwards as a result of blood pressure. The bulge is known as an aneurysm.

Aneurysms do not usually cause any noticeable symptoms unless the wall of the blood vessel becomes so weak that it enlarges or ruptures, which can place pressure on nearby areas and can sometimes lead to internal bleeding or organ dysfunction.

The symptoms of a ruptured aneurysm can vary depending on where in the body the aneurysm developed. Possible symptoms include:

• pain in a limb
• a sudden agonising headache
• dizziness
• breathlessness
• coughing up blood
• confusion
• loss of consciousness

Inflammation of the nervous system

Inflammation of the central nervous system (CNS) causes the most serious symptoms associated with Behçet's disease.

The symptoms of CNS inflammation usually develop quickly over the space of a few days, and can include:

• headache
• double vision
• loss of balance
• seizures (fits)
• partial paralysis on one side of the body
• behavioural or personality changes

General symptoms

In addition to the more specific symptoms above, it is also common for people with Behçet's disease to experience more general symptoms as a result of the condition, including periods of extreme physical or mental tiredness (fatigue). This can affect a person's ability to perform any sort of activity.