Not All Drug Reactions Are the Same: How SJS/TEN Differs from OtherMedication Reactions

By Kimia Ameri and Aziz Ghafoor August 28th, 2026

Every medication has the potential to cause side effects, and although most people tolerate

medications without issue, some individuals may develop a reaction affecting the skin. The term ''drug rush'' is often used broadly, but in reality, drug reactions exist on a wide spectrum. Some are mild, uncomfortable, and resolve once the medication is stopped, while others are rare, life-threatening medical emergencies requiring immediate hospitalization.

Understanding the differences between common drug reactions and severe cutaneous adverse reactions (SCARs) can help patients recognize warning signs and know when to seek urgent medical care. Although Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are among the rarest drug reactions, they are also among the most serious.

Common Drug Reactions Most medication-related skin reactions are mild and improve after the offending medication is discontinued. While they should always be discussed with a healthcare provider, they generally do not cause permanent damage.

1. Maculopapular (Exanthematous) Rash

The most common type of drug reaction is a maculopapular (or exanthematous) eruption.

It usually appears 1-2 weeks after starting a new medication and presents as widespread

flat red patches with small raised bumps, most often beginning on the trunk before

spreading to the arms and legs. These rashes are often mildly itchy but are typically not

painful and rarely involve the mouth, eyes, or other mucous membranes. Most cases

resolve within days to weeks after the medication is stopped. 1,2stopped. 1,2

2. Urticaria (Hives)

Urticaria, commonly known as hives, consists of raised, intensely itchy welts that can

appear within minutes to hours after taking a medication. The rash often changes location

throughout the day and may be accompanied by swelling of the lips, eyelids, or face

(angioedema). Although hives themselves are usually not dangerous, swelling involving

the tongue or throat, difficulty breathing, or symptoms of anaphylaxis require immediate

emergency medical attention.¹ ,2

3. Fixed Drug Eruption

A fixed drug eruption is a distinctive reaction that causes one or several sharply defined

red or purple patches that repeatedly develop in the same location whenever the

responsible medication is taken. After healing, these areas often leave behind dark discoloration of the skin. While uncomfortable, fixed drug eruptions are generally

localized and much less severe than SJS/TEN. ¹ ,2 Severe Cutaneous Adverse Reactions (SCARs) A small proportion of medication reactions belong to a group known as severe cutaneous adverse reactions (SCARs). Unlike common drug rashes, SCARs are medical emergencies because they may affect not only the skin, but also the eyes, mouth, internal organs, and immune system. Prompt recognition and immediate discontinuation of the offending medication are critical. 3

1. Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN)

SJS and TEN are rare but potentially life-threatening reactions in which the immune

system attacks the skin and mucous membranes. Symptoms often begin with fever,

fatigue, sore throat, or flu-like symptoms, followed by the development of painful red or

purple skin lesions that blister and peel. Painful sores commonly affect the mouth, eyes,

nose, and genital area, and extensive skin loss may occur. 1,3,4

Doctors distinguish SJS and TEN based on the amount of skin detachment. SJS involves

less than 10% of the body surface area, TEN involves more than 30%, and cases between

these ranges are considered SJS/TEN overlap. Because these reactions can rapidly

progress and affect multiple organs, patients typically require care in specialized burn

units or intensive care settings. 1,3,4

2. DRESS Syndrome

Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) is another severe

delayed drug reaction. Unlike SJS/TEN, DRESS usually develops 2-8 weeks after

starting a medication, making it one of the latest drug reactions to appear. Patients often

develop a widespread rash together with fever, facial swelling, enlarged lymph nodes,

abnormal blood tests, and inflammation of internal organs, particularly the liver.

Recovery can take weeks to months, and careful long-term follow-up is often required.¹ ,3,5

3. Acute Generalized Exanthematous Pustulosis (AGEP)

AGEP is characterized by the sudden appearance of hundreds of tiny, sterile pustules on

red, swollen skin, usually accompanied by fever. Unlike DRESS, AGEP often develops

within one to several days of starting the offending medication. Although the rash can

appear dramatic, it usually improves rapidly after the medication is stopped and is

generally associated with a better prognosis than SJS/TEN or DRESS.¹ ,3,6

How Is SJS/TEN Different?

Although SJS/TEN may initially resemble a common drug rash, several warning signs

distinguish it from more typical medication reactions.

Feature	Common Drug Rash	SJS/TEN
Skin is itchy	Often	Sometimes
Skin is painful	Rare	Common
Fever	Uncommon	Common
Blisters	Rare	Common
Mouth or eye sores	Rare	Common
Skin peeling	Rare	Common
Requires emergency care	Usually no	Yes

One of the most important differences is that SJS/TEN is typically painful rather than simply

itchy. Many patients experience skin tenderness before blisters even appear. Painful sores

affecting the mouth, eyes, or genitals, together with fever or flu-like symptoms, should never be ignored, particularly if a new medication was started within the previous several weeks. 1,3.

When Should You Seek Emergency Care?

Most medication rashes are not emergencies, but you should seek immediate medical attention if a new rash develops after starting a medication and is accompanied by:

• Fever or flu-like symptoms

• Painful skin

• Blisters or skin peeling

• Painful sores in the mouth, eyes, or genital area

• Eye redness, pain, or changes in vision

• Difficulty swallowing or eating

• Rapidly spreading rash

• Feeling significantly unwell

Early recognition and prompt discontinuation of the offending medication can be lifesaving in

severe drug reactions.

Final Thoughts

Most drug-related skin reactions are mild and resolve after the offending medication is

discontinued. However, severe cutaneous adverse reactions such as SJS/TEN, DRESS, and

AGEP are fundamentally different conditions that require urgent medical evaluation. Knowing the warning signs, particularly painful skin, mucosal involvement, fever, and blistering, can help patients seek care before these reactions progress.

References

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cutaneous adverse drug reactions. British Journal of Clinical Pharmacology. 2024

Aug;90(8):1838-55.

2. Crisafulli G, Franceschini F, Caimmi S, Bottau P, Liotti L, Saretta F, Bernardini R,

Cardinale F, Mori F, Caffarelli C. Mild cutaneous reactions to drugs. Acta Bio-Medica:

Atenei Parmensis. 2019 Jan 28;90(3-S):36-43.

3. Tempark T, John S, Rerknimitr P, Satapornpong P, Sukasem C. Drug-induced severe

cutaneous adverse reactions: insights into clinical presentation, immunopathogenesis,

diagnostic methods, treatment, and pharmacogenomics. Frontiers in pharmacology. 2022

Apr 20;13:832048.

4. Watanabe H, Ogawa Y, Yamaguchi Y, Nakajima S, Mizukawa Y, Mushiroda T, Takahashi

H, Fujiyama T, Sotozono C, Kaneko Y, Hasegawa A. Guidelines for the management of

stevens–johnson syndrome and toxic epidermal necrolysis 2025 supplement. The Journal

of Dermatology. 2026 Feb;53(2):e88-101.

5. Calle AM, Aguirre N, Ardila JC, Villa RC. DRESS syndrome: a literature review and

treatment algorithm. World Allergy Organization Journal. 2023 Mar 1;16(3):100673.

6. Thienvibul C, Vachiramon V, Chanprapaph K. Five‐year retrospective review of acute

generalized exanthematous pustulosis. Dermatology Research and Practice.

2015;2015(1):260928.