Why does drug rash cause skin rash?

The immune system may recognise a medicine, or a substance formed from it, as a trigger. Chemical messengers then cause blood vessels and nearby skin cells to react. This can create flat or raised red areas, itching, swelling, scaling, or small bumps. Some reactions are limited to the skin, while others affect the mouth, eyes, breathing, or internal organs. A rash may appear after a new prescription, a dose change, or exposure to a medicine used before.

Write down the medicine name, dose, start date, and the time the rash appeared. Include non-prescription pain relievers, antibiotics, vitamins, and supplements. Contact the prescriber before taking another dose of a suspected medicine; the correct plan depends on the medicine and your health. Use gentle skin care, avoid scratching, and do not apply a new medicated cream without advice, since it may obscure the rash or irritate the skin.

Get emergency care for breathing difficulty, facial or tongue swelling, dizziness, blistering, skin tenderness, peeling, purple spots, or sores on the lips, mouth, eyes, or genitals. A rapidly spreading rash or fever should be assessed promptly, particularly after starting a new medicine.

Ask whether the reaction fits a drug rash, which medicine should be avoided, and whether the event belongs in your medical record as an allergy or intolerance. Ask what to use for itching and which changes mean you should return urgently.