A methotrexate rash can take several different forms, from flat red patches and raised bumps to blisters, peeling skin, or open sores. The appearance depends on what type of skin reaction is occurring. Most commonly, people notice red, slightly raised spots (a maculopapular rash) that may itch or burn. These reactions typically appear one day to three weeks after starting the medication or after a dose change, and they tend to resolve within one to two weeks once the drug is stopped.
Common Rash Types and How They Look
Methotrexate can trigger a range of skin reactions. The most frequently reported is a maculopapular eruption: flat red spots mixed with small raised bumps, often scattered across the trunk, arms, or legs. This type of rash may be mildly itchy or completely painless, and it can spread over several days.
Other recognized patterns include hives (raised, itchy welts that shift location), papular eruptions (clusters of small firm bumps), and erythema multiforme, which produces distinctive target-shaped red lesions. Some people develop vasculitis-related rashes, where inflammation of small blood vessels creates purplish or dark red spots, particularly on the lower legs.
In more serious cases, the skin can develop well-defined, irregularly shaped ulcers with dark crusting on the surface, surrounded by red, scaly skin. These ulcers tend to appear on the trunk and extremities and can vary widely in size. When a skin biopsy is performed on these lesions, it shows sharply defined areas where the outer skin layer has broken down. The development of skin erosions or ulceration during methotrexate treatment has been described as a potential warning sign of serious blood count problems, so these deserve prompt medical attention.
Injection Site Reactions
If you take methotrexate by injection, you may notice reactions at the spot where the needle went in. These typically appear as bright red patches or small red bumps on the skin. At first the area looks inflamed and red, and over time it fades to a darker, brownish discoloration that can linger for weeks or months. Most people who inject into the thighs see these marks on the front of both legs. In rare cases, the injection site can develop a small ulcer or a more textured, rough-surfaced skin reaction, but simple red patches are far more common.
Photosensitivity Reactions
Methotrexate makes your skin more sensitive to sunlight, and this effect occurs at both low and high doses. A photosensitivity reaction looks and feels like a severe sunburn, but it develops after sun exposure that wouldn’t normally cause you problems. The affected skin turns red and may develop small raised bumps, blisters, swelling, or oozing lesions. These reactions are limited to sun-exposed areas like the face, neck, forearms, and hands, which helps distinguish them from other types of methotrexate rash. Wearing sunscreen and protective clothing during treatment significantly reduces this risk.
Signs of a Severe Skin Reaction
Methotrexate is associated with rare but dangerous skin reactions, including Stevens-Johnson syndrome and toxic epidermal necrolysis. These conditions start with flu-like symptoms and progress to widespread skin involvement. Early warning signs include red or purplish flat spots that spread quickly, painful blisters, peeling skin, and erosions inside the mouth, eyes, or genitals. One case report documented a patient who developed a spreading red, bumpy rash with blood crusting covering roughly 10 percent of their body, along with bleeding from the eyes and mouth, about two weeks after initial symptoms appeared.
Distinguishing these severe reactions from other conditions sometimes requires an urgent skin biopsy. Patients presenting with eye inflammation (conjunctivitis), spreading red spots, and mucosal erosions need rapid evaluation because Stevens-Johnson syndrome and toxic epidermal necrolysis can be fatal without immediate treatment. Pfizer’s prescribing information for methotrexate lists skin necrosis, exfoliative dermatitis, and these severe blistering conditions among the dermatologic reactions that warrant stopping the medication.
Drug Rash vs. Disease Flare
One of the trickiest aspects of a methotrexate rash is telling it apart from a flare of the condition being treated. People taking methotrexate for psoriasis, for example, can develop ulcerated psoriatic plaques or erosions of existing psoriasis patches as a direct drug reaction, not a worsening of their disease. The key differences to watch for: a drug reaction tends to appear in new locations (not just where you normally have symptoms), develops on a timeline that corresponds to a dose change, and may involve skin textures you haven’t seen before, like blisters or dark crusting. A disease flare more often intensifies in your usual problem areas and looks like a more severe version of what you already know.
Timing is one of the most useful clues. Since methotrexate skin reactions generally begin within one day to three weeks of starting the drug or adjusting the dose, any new rash in that window deserves a closer look. If the rash resolves after the medication is held, that strongly suggests the drug was responsible.
What to Watch For
Any new or worsening skin change during methotrexate treatment warrants a call to your prescriber. Contact them promptly if you notice a rash accompanied by itching, fever, or hives. Seek immediate medical care if the rash includes blisters, peeling skin, sores inside the mouth or eyes, or difficulty breathing. Skin reactions during methotrexate treatment can sometimes signal broader toxicity affecting bone marrow or other organs, so even a rash that seems minor on the surface can carry important information about how your body is processing the drug.