Behçet’s disease shows up most visibly as painful mouth sores, genital ulcers, and skin lesions, though it can also cause red, irritated eyes and swollen veins beneath the skin. Every person with Behçet’s gets oral ulcers, and about 95% develop genital ulcers as well. The disease cycles through flares and remissions, so these signs come and go, sometimes looking dramatically different from one week to the next.
Mouth Sores: The First and Most Common Sign
Oral ulcers are the hallmark of Behçet’s disease and often the very first symptom to appear, sometimes years before anything else develops. They look almost identical to common canker sores, which is one reason the disease goes undiagnosed for so long. They start as small, raised round bumps inside the mouth, then quickly break open into painful ulcers.
Up close, these sores are round or oval with slightly rolled edges, covered by a white or grayish film, and surrounded by a red ring of inflamed tissue. They tend to cluster on the inner lips, tongue, and soft palate. What sets them apart from ordinary canker sores is their frequency and persistence: most people with Behçet’s get multiple sores at once, and they recur at least three times a year. A single canker sore that shows up once or twice a year is not the same picture.
Genital Ulcers and Scarring
Genital ulcers in Behçet’s look similar to the oral sores but tend to be larger, deeper, and more destructive. In men, they commonly appear on the scrotum, the junction between the penis and scrotum, and along the penile shaft. In women, they typically develop on the vulva. These lesions have sloping edges and the same whitish covering seen in oral ulcers, but they dig further into the tissue.
The key visual difference from mouth sores is scarring. Oral ulcers usually heal without leaving a mark. Genital ulcers frequently leave visible scar tissue behind, even after they’ve fully resolved. If you looked at the skin between flares, you might see pale, smooth patches of scar from previous episodes alongside fresh, active ulcers. This scarring pattern is distinctive enough that it helps clinicians distinguish Behçet’s from other causes of genital ulceration, like herpes or syphilis.
Skin Lesions: Two Distinct Patterns
Roughly half to three-quarters of people with Behçet’s develop skin problems, and these take two main forms.
The first is red, tender nodules on the shins, a pattern called erythema nodosum. These look like deep, painful bruises beneath the skin, typically a few centimeters across, and they feel firm and warm to the touch. They show up most often on the lower legs but can also appear on the arms, face, and neck. They’re not unique to Behçet’s (they occur in other inflammatory conditions too), but when combined with oral and genital ulcers, they’re a strong clue.
The second pattern resembles acne: clusters of papules and pustules that can appear on the back, chest, and face. These look like inflamed red bumps and whiteheads, and in isolation, they’d be easy to mistake for ordinary acne. The difference is their distribution and context. In Behçet’s, these breakouts are often more widespread, and people who also have joint inflammation tend to have significantly more papules and pustules than the general population. If you’re seeing acne-like breakouts in unusual locations (like the legs or arms) alongside other Behçet’s symptoms, that’s a meaningful pattern.
What Happens to the Eyes
About 35 to 49% of people with Behçet’s develop eye inflammation, and this is the symptom that causes the most lasting damage. The eye involvement doesn’t always look dramatic from the outside, but when it does, the signs are distinctive.
Inflammation at the front of the eye causes visible redness, tearing, and sensitivity to light. In severe cases, a layer of white or yellowish fluid settles at the bottom of the iris, visible as a horizontal line across the lower portion of the colored part of the eye. This fluid layer shifts when you tilt your head, creating a smooth, gravity-dependent line that’s unlike anything seen in typical pink eye or allergies. It’s one of the more visually striking signs of Behçet’s, though it occurs only in severe flares.
Inflammation at the back of the eye is harder to see from the outside. It may cause no visible redness at all, showing up instead as blurred vision or floating spots. This form is particularly dangerous because it can silently damage the retina.
Vascular Signs Visible on the Skin
Behçet’s can inflame blood vessels throughout the body, and one of the visible consequences is superficial blood clots in veins just under the skin. These appear as red or discolored streaks or cords along the leg, warm and tender to the touch, with noticeable swelling in the surrounding area. About 17% of Behçet’s patients develop venous blood clots. Unlike the ulcers and skin lesions, vascular signs can migrate, appearing in one spot, resolving, and then showing up somewhere else.
How Behçet’s Is Identified
There’s no single blood test for Behçet’s disease. Diagnosis relies on recognizing the pattern of symptoms. Under the current international criteria, oral ulcers, genital ulcers, and eye inflammation each carry the most diagnostic weight, while skin lesions, nervous system involvement, and vascular problems carry somewhat less. A combination of these findings, when they add up sufficiently, leads to a diagnosis.
One unusual diagnostic tool is the pathergy test, where a doctor pricks the skin with a needle and checks the site 24 to 48 hours later. In most people, a needle prick heals with minimal reaction. In Behçet’s, the skin overreacts: a red, raised bump (2 to 3 millimeters or larger) forms at the puncture site, sometimes progressing to a small pustule. This exaggerated wound response reflects the same underlying process that drives the ulcers and skin lesions elsewhere on the body. The bumps peak at 48 hours and gradually fade over several weeks. Not everyone with Behçet’s tests positive (only about 14 to 21% do in U.S. populations), so a negative result doesn’t rule it out.
How Symptoms Change Over Time
Behçet’s disease is unpredictable. Flares can involve one system or several at once, and the severity changes over the years. Oral ulcers tend to be the most persistent feature, while eye and vascular involvement typically develop within the first few years of disease. Many people notice that flares gradually become less frequent and less severe over time, particularly after the first decade. The scarring from genital ulcers and the potential for permanent vision loss from repeated eye inflammation, however, are cumulative, which is why early recognition matters.