Behcet’s disease is not contagious. You cannot catch it from someone who has it, and a person with the condition cannot spread it through physical contact, saliva, blood, or sexual activity. The confusion is understandable: Behcet’s causes painful mouth sores and genital ulcers that can look remarkably similar to herpes or other infections that are contagious. But the underlying cause is completely different.
Why It Looks Contagious but Isn’t
The hallmark symptoms of Behcet’s disease, especially recurring oral and genital ulcers, closely resemble lesions caused by herpes simplex virus. This visual similarity is one of the main reasons people worry about transmission, and it’s also why doctors must carefully distinguish between the two conditions. In herpes, a virus invades cells and can be passed to others. In Behcet’s, the immune system itself is causing the damage. No virus or bacterium is being shed from those sores, so there is nothing for another person to “catch.”
What Actually Causes It
Behcet’s is classified as an autoinflammatory vasculitis, which means the immune system attacks the body’s own blood vessels. It can affect arteries and veins of all sizes throughout the body. Certain immune cells, particularly a type of white blood cell called T-helper cells, become overactivated and flood tissues with inflammatory signals. This triggers a chain reaction: other immune cells rush to the area, and the resulting inflammation damages blood vessel walls and surrounding tissue.
The painful mouth sores, skin pustules, and other surface-level symptoms happen because a specific type of white blood cell (neutrophils) becomes hyperactive and creates a damaging inflammatory reaction in small blood vessels near the skin and mucous membranes. It’s essentially friendly fire from your own immune system, not an outside invader.
The Role of Genetics
While Behcet’s isn’t inherited in a straightforward way, genetics play a significant role in who develops it. The strongest known genetic link is a marker called HLA-B51. In countries where Behcet’s is common, 50 to 80% of patients carry this marker, compared to roughly 13 to 29% of the general population. Carrying HLA-B51 increases the odds of developing the disease by 5 to 10 times in those regions.
Family history matters, too, though the risk is moderate. About 1 to 18% of patients report a relative with the condition, with higher rates in Turkish, Israeli, and Korean families. In Turkey, the sibling recurrence risk is around 4.2%, and siblings of someone with Behcet’s are estimated to be 11 to 52 times more likely to develop it than the general population. That said, most people with a family member who has Behcet’s will never develop it themselves. The genetic component creates susceptibility, not certainty.
Environmental Triggers in Genetically Susceptible People
The current understanding is that Behcet’s develops when an environmental trigger sets off an abnormal immune response in someone who is already genetically predisposed. Certain common bacteria and viruses have been investigated as possible triggers, including oral streptococcal bacteria and herpes simplex virus-1 (HSV-1). The theory is that these microbes contain proteins that resemble the body’s own tissue. When the immune system mounts a response against the microbe, it accidentally learns to attack similar-looking proteins on the body’s own blood vessel walls. This process is called molecular mimicry.
Importantly, the infection itself doesn’t cause the disease. Once the immune system has been misdirected, the inflammatory process continues even after the original infection is gone. Poor oral health has been noted more frequently in Behcet’s patients, which may increase exposure to the bacterial triggers that kickstart this process. But again, the bacteria involved are common ones that most people encounter without ever developing Behcet’s. It takes the right genetic background for the immune system to go off course.
Who Gets Behcet’s Disease
Behcet’s follows a striking geographic pattern. It’s most common along the ancient Silk Road trading route stretching from East Asia to the Mediterranean. Turkey has the highest prevalence by far at 421 cases per 100,000 people. Iran follows at 80 per 100,000, then Saudi Arabia at 20, Iraq at 17, and Japan at about 13.5. In Western countries, rates drop sharply: 7.1 per 100,000 in France, 5.2 in the United States, and under 1 in the United Kingdom. This geographic clustering supports the idea that specific genetic backgrounds, combined with regional environmental exposures, drive the disease.
How It’s Diagnosed
There’s no single blood test for Behcet’s. Doctors use a point-based system called the International Criteria for Behcet’s Disease. Oral ulcers, genital ulcers, and eye inflammation each earn 2 points. Skin lesions, nervous system involvement, and blood vessel problems each earn 1 point. A score of 4 or more points leads to a Behcet’s classification. Because the symptoms overlap with infections and other autoimmune conditions, diagnosis often takes time and requires ruling out other causes first.
How It’s Managed
Treatment focuses on calming the overactive immune system and controlling flares. During acute episodes, corticosteroids are commonly used to quickly reduce inflammation, especially when the eyes, joints, or nervous system are involved. For long-term management, immunosuppressant medications help keep the immune response in check and reduce flare frequency.
When standard treatments aren’t enough, biologic therapies that target specific inflammatory signals can be effective. These include drugs that block TNF (a key inflammation-promoting molecule), as well as medications targeting other immune signaling proteins like interleukin-1, interleukin-6, and interleukin-17. The choice of treatment depends on which organs are affected and how severe the symptoms are. Many people with Behcet’s go through cycles of flares and remission, and treatment plans often evolve over time as doctors adjust to the disease’s pattern in each individual.