ConditionSkin, hair & nails
Drug-Induced Eruptions (Drug Rash)
Drug-induced eruptions are skin rashes caused by a medicine. The most common is a widespread red, blotchy, itchy rash (morbilliform or "measles-like" rash) that appears 4 to 14 days after starting a drug and fades once it is stopped. Other types include hives, fixed drug eruptions and sun-sensitivity reactions. Rarely, a drug rash is the start of a severe reaction such as Stevens-Johnson syndrome or DRESS, which causes blistering, mouth sores, fever or facial swelling and needs emergency care.
Also called: Drug rash, drug eruption, cutaneous adverse drug reaction, medication rash, drug allergy rash
At a glance
- What it is
- A skin reaction triggered by a medicine, ranging from mild to life-threatening.
- Most common type
- Morbilliform (measles-like) rash 4 to 14 days after starting a drug.
- Common culprits
- Antibiotics (penicillins, sulfonamides), anti-seizure drugs, allopurinol, NSAIDs.
- Red flags
- Blisters, peeling, mouth or eye sores, fever, facial swelling, painful skin.
- Treatment
- Stop the drug (with your prescriber), antihistamines and steroid creams for mild rashes; hospital care for severe reactions.
When to get help
Call 911 or go to the ER
- Swelling of the lips, tongue or throat, wheezing, trouble breathing or fainting (anaphylaxis): use epinephrine if prescribed and call 911
- Blisters, peeling skin, or painful, dusky red or purple skin, especially with sores in the mouth, eyes or genitals (possible SJS or TEN)
- A widespread rash with high fever, facial swelling, swollen glands or yellow skin, 2 to 8 weeks after starting a new drug (possible DRESS)
See a doctor within a day or two
- A new widespread rash while taking a medicine, even if mild; contact your prescriber the same day about stopping it
- A rash with fever, joint pain or feeling unwell
- Hives that keep spreading over hours
Book a routine appointment
- A recurring round, dark patch in the same spot each time you take a certain medicine (fixed drug eruption)
- A rash on sun-exposed skin after starting a new medicine
- A past rash labeled as "penicillin allergy" that you would like reviewed
Usually safe to manage at home
- Mild itch and a few spots after a vaccine or a new medicine has already been stopped on medical advice, with no fever and no blisters
Types of drug eruption
| Type | What it looks like | Typical timing | Severity |
|---|---|---|---|
| Morbilliform (exanthematous) | Flat and raised red spots merging into blotches, starting on trunk, itchy | 4 to 14 days after starting | Usually mild |
| Hives (urticaria) | Raised, itchy welts that move around, sometimes with swelling | Minutes to hours | Can be part of anaphylaxis |
| Fixed drug eruption | One or a few round, dusky patches that recur in the same place | Hours after each dose | Mild, leaves dark marks |
| Photosensitivity | Sunburn-like rash on sun-exposed skin | After sun exposure | Mild to moderate |
| Stevens-Johnson syndrome / TEN | Painful dusky skin, blisters, peeling, mouth and eye sores | 4 to 28 days | Life-threatening |
| DRESS | Widespread rash, facial swelling, fever, swollen glands, organ inflammation | 2 to 8 weeks | Life-threatening |
| AGEP | Many tiny pustules on red skin, fever | 1 to 5 days | Usually resolves quickly |
| Serum sickness-like reaction | Hives, joint pain, fever | 1 to 3 weeks | Moderate |
Common culprit medicines
- antibiotics: amoxicillin and other penicillins, cephalosporins, sulfonamides (trimethoprim-sulfamethoxazole)
- anti-seizure medicines: carbamazepine, phenytoin, lamotrigine
- allopurinol for gout
- NSAIDs such as ibuprofen and naproxen
- some HIV medicines, such as nevirapine and abacavir
- contrast dye, chemotherapy and immunotherapy drugs
- diuretics, tetracyclines and some blood pressure medicines (photosensitivity)
Amoxicillin given during infectious mononucleosis often causes a widespread rash that is not usually a true allergy.
Why drug rashes happen
Most drug eruptions are immune reactions. Hives and anaphylaxis are rapid, IgE-mediated allergic reactions. Morbilliform rashes, SJS and DRESS are delayed reactions driven by T cells. Some reactions are linked to specific genes, such as HLA-B*15:02 and carbamazepine in people of Asian ancestry, or HLA-B*58:01 and allopurinol. Genetic screening is recommended before starting some of these drugs in at-risk groups.
Diagnosis
A doctor will ask about every medicine, supplement and vaccine taken in the past 8 weeks, with start dates, and examine the skin, mouth, eyes and lymph nodes. Clues include the timing, the pattern of the rash and improvement after stopping the drug. Tests may include:
- blood count (eosinophils), liver and kidney function, especially when DRESS is suspected
- skin biopsy for severe or unclear rashes
- later, allergy testing (skin tests or supervised drug challenge) to confirm or remove an allergy label, mainly for penicillins
Treatment
Stop the drug
The most important step. Contact your prescriber before stopping essential medicines such as anti-seizure drugs, so they can switch you safely.
Mild rashes
- oral antihistamines for itch
- moisturizers and cool compresses
- topical steroid creams for a few days
- the rash usually fades within 1 to 2 weeks after stopping, often with some peeling
Severe reactions
- anaphylaxis: epinephrine injection and emergency care
- SJS/TEN: hospital admission, often in a burn or intensive care unit, with wound care, eye care, fluids and pain control
- DRESS: hospital care and usually systemic steroids, with monitoring of the liver, kidneys and heart
After a drug rash
- Record the drug and reaction type in your medical record and tell every prescriber and pharmacist.
- Carry a list or wear a medical alert bracelet for severe reactions.
- Never take the drug again after SJS, TEN or DRESS.
- For mild reactions to penicillin, ask about allergy testing. Most people with a penicillin allergy label are not truly allergic, and removing the label opens up better antibiotic choices.
Frequently asked questions
What does a drug rash look like?
The most common drug rash is a widespread pattern of red, flat or slightly raised spots that merge into blotches, often starting on the trunk and itching. Other drug rashes appear as hives, dark round patches that recur in one spot, sunburn-like areas, or, rarely, blisters and peeling.
How long does a drug rash last?
A typical morbilliform drug rash fades within 1 to 2 weeks after the medicine is stopped, often with mild peeling. Severe reactions such as DRESS can last weeks to months. A rash that keeps worsening after stopping the drug needs review.
How soon after taking a medicine can a rash appear?
Hives can appear within minutes to hours. Most morbilliform rashes appear 4 to 14 days after starting a medicine. SJS usually starts within 4 weeks, and DRESS 2 to 8 weeks after starting a drug. Rashes can appear after the course has finished.
When is a drug rash an emergency?
It is an emergency if you have swelling of the lips, tongue or throat, difficulty breathing, blisters or peeling skin, sores in the mouth or eyes, painful skin, or a rash with high fever and facial swelling. Call 911 or go to the ER.
Sources
This guide was written from current patient and clinical guidance, including:
- American Academy of Dermatology: Drug rashes
- American Academy of Allergy, Asthma & Immunology: Drug Allergy
- MedlinePlus: Drug allergies
- AAAAI/ACAAI Joint Task Force: Drug Allergy, A 2022 Practice Parameter Update
- NHS: Drug allergy
- Genetic and Rare Diseases Information Center: Stevens-Johnson syndrome/toxic epidermal necrolysis