Rash During Cancer Treatment

Rash during cancer treatment has many possible causes. Targeted therapy, immunotherapy, chemotherapy, radiation, infection, allergy, adhesives, antibiotics, and other medicines can all bring one on. The look of the rash and its timing help the care team narrow the cause.

This page is a planning aid. It cannot diagnose a symptom or replace the instructions from your oncology team.

Some rashes are uncomfortable but easy to manage. Others can signal allergy, infection, a severe skin reaction, or immune-related inflammation. Photos and a medicine timeline can make the visit much more useful.

Many treatment side effects are easier to handle when the team hears about them early. If your team already gave you an urgent call plan, use that plan first.

• where the rash is and whether it is spreading.
• itching, pain, blisters, peeling, mouth sores, fever, swelling, or drainage.
• new medicines, antibiotics, contrast dye, supplements, adhesives, or skin products.
• treatment type, radiation area, and most recent treatment date.
• clear photos over time, if comfortable and allowed by your care team.

• What is the most likely cause in my situation, and what else needs to be ruled out?
• Which symptoms or changes mean same-day contact for my exact treatment?
• What should I track before I call or come in?
• Could this affect treatment timing, dose, or supportive medicines?
• Who should I contact after hours, and what should I say first?

The plan may include skin care, prescription creams, or oral medicines. It may also include a check for infection, an allergy review, a change to the treatment schedule, dermatology input, or urgent assessment for severe patterns.

Ask what would change the plan. Ask what can simply be watched, and what should not wait until the next routine visit.

• Do not assume a symptom is "just treatment" without checking the plan your team gave you.
• Do not assume the same symptom means the same thing for every cancer treatment.
• Do not start a new over-the-counter medicine, supplement, or major diet change while symptoms are active. Ask the care team first.

• Call 911 or go to an emergency department if the rash comes with trouble breathing, swelling of the face, lips, or tongue, or feeling faint.
• Call 911 or go to an emergency department if the skin is blistering and peeling away, or if painful sores appear in your mouth, eyes, or genitals along with a fever. Severe skin reactions such as Stevens-Johnson syndrome start this way. They need hospital care.
• Call your care team the same day if the rash is spreading quickly, is painful, is blistering, or covers a large area of skin.
• Ring your cancer team right away, whatever the hour, if the rash comes with a temperature of 100.4°F (38°C) or higher, or with chills, and you are having chemotherapy. Fever on chemotherapy is an emergency in the CDC's guidance, whatever the skin is doing. If you cannot reach them quickly, go to an emergency department and tell staff you are on chemotherapy.
• Call your care team the same day if the rash comes with that same temperature or with chills and chemotherapy is not part of your treatment. Report a rash on immunotherapy the same day if it involves your eyes or the lining of your mouth.
• Call your care team within a day or two if the rash is itchy or sore enough to disturb sleep, or is not settling with the skin care you were given. Do the same if an area becomes newly red, warm, swollen, or weeping.

Helpful next pages include Rash During Immunotherapy, Radiation Dermatitis: Skin Care Questions, Immune-Related Side Effects, and Side Effects of Cancer Treatment.

• National Cancer Institute, Skin and Nail Changes During Cancer Treatment, accessed August 11, 2026
• National Cancer Institute, Infection and Neutropenia During Cancer Treatment, accessed August 11, 2026
• StatPearls (NCBI Bookshelf), Stevens-Johnson Syndrome, accessed August 11, 2026