Methotrexate is frequently listed as a photosensitizing drug, but the reality is more nuanced than a simple yes. The UK’s medicines regulator (MHRA) has flagged the risk of serious photosensitivity reactions with both low-dose and high-dose methotrexate. However, the skin reaction methotrexate most commonly causes isn’t traditional sun sensitivity. It’s a distinct phenomenon called radiation recall, where previously sunburned skin flares up again after you start the medication, even without new sun exposure.
Understanding the difference matters because it changes what you watch for and how you protect yourself.
Radiation Recall vs. True Photosensitivity
Most drugs that cause photosensitivity make your skin more vulnerable to sunlight in the moment. You go outside, the drug interacts with UV rays, and you burn faster or develop a rash. Methotrexate works differently. According to Arthritis Research Canada, methotrexate does not cause sunburn. Instead, it irritates areas where you’ve had sunburns in the past.
This is called a radiation recall reaction, sometimes also referred to as a photorecall or photoreactivation reaction. After you start methotrexate, skin that was previously damaged by UV exposure can become inflamed again, producing a sunburn-like eruption in those same areas. The key distinction: this can happen without any new sun exposure at all. Your body essentially “remembers” the old damage, and the drug triggers a repeat inflammatory response in that tissue. This pattern has also been documented with other chemotherapy drugs like docetaxel and gemcitabine, but methotrexate is one of the most commonly associated medications.
When True Photosensitivity Does Occur
While radiation recall is the more typical reaction, methotrexate can also cause genuine photosensitivity in some people. These reactions fall into two categories.
Phototoxic reactions are the more common type. UV radiation activates the drug in your skin and directly damages skin cells, triggering an inflammatory response. This looks like a severe sunburn with redness, swelling, and sometimes blistering in sun-exposed areas. It typically appears within 24 hours of sun exposure, and higher doses of the medication increase the risk. Skin that wasn’t exposed to sunlight stays normal.
Photoallergic reactions are less common but behave differently. These involve the immune system: UV light transforms the drug into a substance your body treats as a foreign invader, setting off a delayed allergic response. A rash appears at least 24 to 48 hours after sun exposure and often looks like eczema. Unlike phototoxic reactions, a photoallergic reaction can spread beyond sun-exposed skin to covered areas of the body. The risk isn’t tied to your dose of methotrexate.
Low-Dose Users Are Not Exempt
If you take methotrexate for rheumatoid arthritis, psoriasis, or another inflammatory condition, you might assume that photosensitivity is only a concern at the higher doses used in cancer treatment. That’s not the case. The MHRA safety update specifically noted that serious photosensitivity reactions can occur with both low-dose and high-dose methotrexate. The radiation recall phenomenon in particular has no clear dose threshold, since it depends on your history of prior sun damage rather than how much medication you’re taking.
What These Reactions Look and Feel Like
Radiation recall typically presents as redness, tenderness, or a sunburn-like rash that appears in areas where you’ve been sunburned before. It can show up days or weeks after starting methotrexate, and the trigger isn’t a day at the beach. It’s the drug itself reactivating old damage.
Phototoxic reactions look like an unusually severe sunburn confined to the areas that were exposed to sunlight. You might notice redness, swelling, and in more serious cases, fluid-filled blisters. These tend to develop quickly, within minutes to hours of UV exposure.
Photoallergic reactions take longer to appear and look more like a spreading, itchy rash or eczema. Because they can extend to skin that was covered by clothing, they’re sometimes mistaken for an unrelated allergic reaction or a flare of an underlying skin condition.
Protecting Your Skin on Methotrexate
Knowing that methotrexate can trigger both recall reactions and genuine photosensitivity means sun protection is worth taking seriously, even if you’ve never thought of yourself as sun-sensitive. A broad-spectrum sunscreen that blocks UVA rays (not just UVB) is important because UVA penetrates deeper into the skin and drives both phototoxic and photoallergic reactions. Protective clothing, hats, and seeking shade during peak UV hours all reduce your exposure.
For radiation recall specifically, prevention is partly retrospective. The reaction targets skin that was already damaged, so there’s no way to undo past sunburns. But minimizing new sun damage reduces the total area of skin that could be vulnerable to recall reactions if your treatment continues or if you start methotrexate again in the future.
If you notice an unexplained sunburn-like rash, especially in areas you haven’t recently exposed to sunlight, radiation recall is a likely explanation. The pattern of the rash, particularly whether it maps onto areas of previous sunburns, is one of the clearest ways to distinguish it from other drug reactions or skin conditions.