Stevens-Johnson Syndrome (SJS): A Life-Threatening Severe Drug Allergy. A Dermatologist Explains the Warning Signs, How to Tell It Apart from an Ordinary Drug Rash, and Which Drugs to Watch
Most drug rashes are not dangerous and clear up once the drug is stopped. But one type of drug rash is a medical emergency and can be fatal: Stevens-Johnson Syndrome (SJS), and its more severe form, TEN. In this article, a dermatologist explains what SJS is, the warning signs that set it apart from an ordinary drug rash, which drugs carry risk, the genetic testing that can help prevent it in Thai people, and what to do right away if you suspect it.
Short summary, the most urgent point: if you take a medicine and develop a rash with fever, sores in the mouth, eyes or genitals, painful or burning skin, or skin peeling off in sheets, stop the suspected drug immediately and go to a hospital or emergency room right away. Do not wait and watch, because this may be SJS/TEN, and the later it is treated, the more dangerous it becomes.
What is Stevens-Johnson Syndrome (SJS)?
Stevens-Johnson Syndrome (SJS) is a severe drug allergic reaction that causes inflammation of the skin and mucous membranes (mouth, eyes, genitals), blistering, and skin that peels off in sheets, similar to a scald burn. It occurs when the immune system reacts abnormally to certain drugs (in some cases it is triggered by an infection).
SJS belongs to the same disease spectrum as TEN (Toxic Epidermal Necrolysis), which is the same condition in a more severe form. They are classified by the area of skin that peels off:
SJS: skin peeling affects less than 10% of the body surface.
SJS/TEN overlap: 10-30% peeling.
TEN: peeling affects more than 30%. This is the most dangerous form.
Although it is a rare disease, it has a high death rate, especially TEN, so it is always a medical emergency that must be treated in a hospital.
The international disease code for SJS is ICD-10 L51.1 (Stevens-Johnson syndrome).
Warning signs: how to tell SJS apart from an ordinary drug rash
This is the heart of the article. Most drug rashes are not SJS and go away on their own once the drug is stopped, but knowing when a rash is dangerous can save a life.
An ordinary (mild) drug rash usually looks like this
A red rash that is flat or slightly raised, spread over the body, and usually itchy.
No large blisters and no peeling skin.
Lips, inside of the mouth and eyes are normal, with no sores.
No high fever, and you generally feel well.
It usually improves once the causative drug is stopped.
Danger signs that suggest SJS/TEN: if you have any one of these, go to a hospital immediately
Fever, body aches and sore throat before or together with the rash (flu-like early symptoms).
Sores on the mucous membranes, especially mouth sores, lips that crack and form bloody crusts, red painful eyes, or genital sores.
Unusually painful or burning skin, hurting even at a light touch (unlike an ordinary rash, which is usually itchy).
Blisters, skin peeling in sheets, or the top layer of skin coming off when rubbed (Nikolsky sign).
A target-shaped rash (target lesion) or a dark-colored rash that spreads quickly, especially on the face and upper body.
You started a new drug within the last 1-4 weeks.
A simple rule to remember: drug rash + fever + sores in the mouth or eyes = think of SJS until proven otherwise. Do not diagnose yourself with just an ordinary rash.
Drugs that most often cause SJS
Most SJS/TEN is caused by drugs, and symptoms usually begin within 1-4 weeks after starting a new drug (in some people up to 8 weeks). Commonly implicated drug groups include:
Anti-seizure drugs such as carbamazepine, phenytoin, lamotrigine, phenobarbital.
Uric acid-lowering drugs / gout treatment, especially allopurinol.
Sulfa drugs (sulfonamides), including some antibiotics.
Antibiotics in the beta-lactam group (such as penicillin) and some other groups.
Pain relievers / anti-inflammatory drugs in the NSAID group, especially the oxicam group.
Some antiviral drugs, such as nevirapine.
A caution that many Thai people overlook: drug packs sold as mixed pills, some herbal remedies, or medicines bought and taken without knowing their ingredients may also contain drugs that cause SJS. Avoid buying medicines to take on your own without consulting a doctor or pharmacist.
Genetic testing before taking a drug: a real way for Thai people to prevent SJS
This is an especially important point for Thai and other Asian people, because the risk of SJS from certain drugs is linked to genes (HLA) that are common in Thai people, and testing before starting the drug can reduce the risk.
HLA-B*15:02 gene: linked to SJS/TEN reactions to the anti-seizure drug carbamazepine. This gene is common in Thai people, so testing for it before starting carbamazepine is recommended. If the gene is found, the doctor will avoid it and use another drug.
HLA-B*58:01 gene: linked to severe reactions to allopurinol (a gout drug). Testing before starting the drug can also help reduce the risk.
These gene tests are available at many hospitals in Thailand. If you are about to start one of these drugs, you can ask your doctor about gene testing first, especially if you have a family history of severe drug allergy.
What to do right away if you suspect SJS
If you or someone close to you has the danger signs above after taking a drug, do the following immediately. Do not wait for the symptoms to get worse.
Stop the suspected drug immediately, especially a drug started within the past 1-4 weeks.
Go to a hospital or emergency room urgently. SJS/TEN must be treated as an inpatient, and some patients need an ICU or a burn unit.
Bring all the medicines you are taking (or photograph the labels) so the doctor can identify the causative drug quickly.
Do not buy creams or oral medicines to treat the rash yourself, because you may get a drug that triggers the allergy again or hides the symptoms.
If you have eye symptoms (eye pain, red eyes), tell the doctor immediately, because SJS affecting the eyes can cause permanent loss of vision if not treated quickly.
Hospital treatment mainly consists of stopping the causative drug, caring for the wounds and fluid-electrolyte balance as in a burn patient, preventing infection, and caring for the eyes, mouth and mucous membranes. Specific drugs (such as steroids, IVIG or cyclosporine) are decided case by case by the doctor and must be given only under a doctor's care.
Complications and long-term care
Even after recovery from the acute phase, SJS/TEN can leave long-term effects, so continued follow-up is needed.
The eyes are the most commonly and most seriously affected organ. Chronic dry eye, scarring of the conjunctiva, and even loss of vision can occur, so you should see an eye doctor early and keep following up.
The skin may have dark spots, uneven color or scars after healing.
Other mucous membranes, such as inside the mouth and the genitals, may develop scarring afterwards.
Psychological effects from such a severe event should also be cared for.
Preventing another drug allergy: what you must do for life
Once you have had SJS from a drug, the body 'remembers' it, and if you receive that drug again the reaction can be even more severe than before. Prevention is just as important as treatment.
Remember the exact name of the drug you are allergic to and always carry a drug allergy card.
Tell your doctor, pharmacist and dentist every time before receiving a new drug that you have had a severe drug allergy.
Be careful with drugs that may cross-react with the drug you are allergic to, and leave that decision to your doctor.
If a close relative has had a severe drug allergy, tell your doctor when starting a risky drug, as gene testing may be considered first.
Good to know: SJS is not contagious and does not spread from person to person. It is an individual reaction of the patient to a drug. So there is no need to worry about catching it, but you must worry about receiving the causative drug again.
Frequently asked questions about SJS (FAQ)
1. What is Stevens-Johnson Syndrome (SJS)?
It is a severe drug allergic reaction that causes inflammation of the skin and mucous membranes (mouth, eyes, genitals), blistering, and peeling similar to a burn. It is a medical emergency that must be treated in a hospital. When more than 30% of the skin peels, it is called TEN, the most severe form.
2. How is SJS different from an ordinary drug rash?
An ordinary drug rash is usually an itchy rash with no fever, a normal mouth and eyes, and it clears when the drug is stopped. SJS usually comes with fever, sores in the mouth or eyes, painful or burning skin, and skin peeling in sheets. If you have these signs, go to a hospital immediately.
3. Which drugs can cause SJS?
It is commonly caused by anti-seizure drugs (carbamazepine, phenytoin, lamotrigine), the gout drug allopurinol, sulfa drugs, some antibiotics, and some NSAIDs. Symptoms usually begin within 1-4 weeks after starting the drug.
4. Can SJS be cured, and how dangerous is it?
It can be treated successfully if you reach the hospital early, but it is a condition with a high death rate, especially TEN, and it may leave long-term complications, particularly in the eyes. Stopping the causative drug quickly and being treated in a hospital are what save lives most.
5. Can gene testing before taking a drug really prevent SJS?
In some cases, yes. Testing for HLA-B*15:02 before using carbamazepine and HLA-B*58:01 before using allopurinol helps identify people at high risk so that another drug can be used instead. These genes are common in Thai people, so you should talk to your doctor before starting these drugs.
6. Is SJS contagious?
No. SJS is not an infection that spreads from person to person. It is an individual reaction to a drug. What you need to watch out for is receiving the causative drug again, which would cause a more severe reaction.
7. What should I do after having SJS?
You must remember the name of the drug you are allergic to, carry a drug allergy card, and tell your doctor or pharmacist every time before receiving a new drug, for life, to avoid receiving the causative drug or a cross-reacting drug again.
Stevens-Johnson Syndrome is a medical emergency in which 'stopping the drug early + reaching a doctor early = always safer'. The information in this article is for basic understanding and cannot replace a doctor's diagnosis. If you suspect a severe drug allergy, especially when fever occurs together with sores in the mouth or eyes, go to a hospital immediately.
Written by Dr. Patara Voravutinon, Dermatologist · Last reviewed July 25, 2026
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