Stevens-Johnson syndrome (SJS) is a rare, severe skin reaction most often triggered by medications. It causes painful blistering and peeling of the skin and affects the mucous membranes of the eyes, mouth, and genitals. If you searched for pictures, you’re likely trying to identify a rash on yourself or someone you know, or trying to understand what this condition actually looks like as it develops. Here’s what causes it, how to recognize it, and what happens as it progresses.
Medications Are the Most Common Cause
The vast majority of SJS cases are triggered by a drug reaction, typically one started within the previous one to three weeks. The most frequently implicated medications include certain anti-seizure drugs (carbamazepine, lamotrigine, phenytoin), the gout medication allopurinol, sulfonamide antibiotics, and some nonsteroidal anti-inflammatory drugs. Less commonly, infections like Mycoplasma pneumonia can trigger SJS, particularly in children.
Not everyone who takes these drugs develops SJS. The reaction is an unpredictable immune response in which the body essentially attacks its own skin cells. What makes one person react while another doesn’t comes down largely to genetics, which is covered below.
Genetics Play a Major Role in Who’s at Risk
Certain inherited immune system markers dramatically increase the risk of SJS from specific drugs. The most well-established link is between a gene variant called HLA-B*15:02 and carbamazepine-induced SJS. This variant is most common in people of Southeast Asian descent: prevalence exceeds 15% in populations from Hong Kong, Malaysia, Thailand, and parts of the Philippines, and is above 5% in Chinese, Taiwanese, Vietnamese, Filipino, and some Indian populations. It’s extremely rare (under 0.1%) in white and Hispanic populations.
Because of this, the FDA recommends genetic screening before starting carbamazepine in patients with ancestry from at-risk populations. A separate variant, HLA-A*31:01, carries a moderate SJS risk and is found more broadly in people of European, Korean, Japanese, and Native American backgrounds. Another variant, HLA-B*58:01, is linked to allopurinol-triggered SJS. These genetic tests are simple blood draws, and knowing your status before starting a high-risk medication can be lifesaving.
What SJS Looks Like as It Develops
SJS doesn’t start with blisters. One to three days before any rash appears, you’ll typically experience what feels like the flu: fever, fatigue, a sore mouth and throat, and burning eyes. These early signs are easy to dismiss, which is part of what makes SJS dangerous. Most people don’t connect these symptoms to a medication they started a week or two earlier.
The rash begins as flat, dark red or purplish spots (macules), often in a target-like pattern with a darker center and lighter ring. These typically appear first on the face, neck, and upper chest, then spread rapidly to other parts of the body. Within one to three days, the spots merge together and form large, fluid-filled blisters with a loose, fragile surface. The skin looks dusky and swollen before it begins to peel.
In more severe cases, sheets of skin can slide off when touched or rubbed, even with light pressure. This is known as the Nikolsky sign, and it’s one of the hallmarks doctors look for during examination. The exposed skin underneath is raw, red, weepy, and extremely painful, similar in appearance to a severe burn.
It Doesn’t Just Affect Skin
One of the features that distinguishes SJS from other drug rashes is its attack on mucous membranes. The lining of the mouth develops painful sores and erosions that can make eating and drinking nearly impossible. The eyes become severely inflamed, red, and crusty, sometimes with damage to the surface of the eye that can lead to long-term vision problems if not treated aggressively. The genital area also develops painful erosions. In many cases, the mucous membrane involvement is actually more distressing and slower to heal than the skin itself.
How SJS Differs From Toxic Epidermal Necrolysis
SJS exists on a spectrum with a more severe condition called toxic epidermal necrolysis (TEN). The distinction is based on how much skin is affected. SJS involves less than 10% of the body’s surface area. When skin detachment covers 10 to 30%, it’s classified as SJS/TEN overlap. At 30% or more, it’s classified as TEN. The conditions share the same underlying mechanism, but TEN carries a significantly higher risk of organ failure and death.
Mortality rates reflect this spectrum clearly. Patients with minimal risk factors have about a 3% chance of dying. As the severity increases, so does the risk: patients with three major risk factors face a mortality rate around 35%, and those with five or more risk factors face mortality above 90%. The factors that predict worse outcomes include age over 40, a faster heart rate, a larger area of skin detachment, and underlying conditions like cancer or diabetes.
How SJS Is Managed
The single most important step is immediately stopping the drug that caused the reaction. Every hour of continued exposure worsens the outcome. Patients with SJS are typically treated in a hospital, often in a burn unit, because the skin damage closely resembles a thermal burn and requires the same careful wound care, fluid replacement, and infection prevention.
Recovery is slow. The skin itself may take two to four weeks to regrow, but complications from eye, mouth, and genital involvement can persist for months. Many SJS survivors deal with lasting effects: chronic dry eyes, light sensitivity, scarring of mucous membranes, skin discoloration, and in some cases, permanent vision impairment. The psychological impact is also significant, with many survivors experiencing anxiety about taking any new medications.
Recognizing the Early Signs
If you’ve recently started a new medication and develop an unexplained fever, sore throat, burning eyes, and fatigue, pay close attention. These prodromal symptoms appear one to three days before the rash and represent the window in which stopping the drug can limit the severity of the reaction. Once target-shaped spots appear or skin begins to blister, the situation is urgent. SJS progresses rapidly, and the difference between a manageable case and a life-threatening one often comes down to how quickly the offending drug is identified and stopped.