Rash and mouth sores on alpelisib

Rash is one of the most common side effects of alpelisib, affecting around a third of people in the main study. It usually appears in the first two to three weeks of treatment, often as red patches with small raised bumps on the chest, back, arms or legs, and it is frequently itchy. Most rashes are mild or moderate, but a smaller number become widespread, and very rarely alpelisib causes severe skin reactions with blistering, peeling skin or sore eyes, which are medical emergencies. Studies found that people who took a non-drowsy antihistamine from the start had less rash and milder rash than those who did not, so many teams now recommend one for the first weeks. Mild rash is treated with antihistamines and steroid creams, while a more widespread rash may need steroid tablets and a pause in alpelisib, then a restart at a lower dose. Mouth sores are less common than rash but still affect a noticeable share of people. They can make eating, drinking and brushing painful. An alcohol-free steroid mouthwash, careful mouth care, a soft toothbrush and bland food help most people. The key message for both problems is the same: report them early. Skin and mouth problems caught quickly are usually easy to control and rarely stop treatment.

Rash is common early

Most rashes appear in the first few weeks of treatment.

Prevention works

A daily antihistamine from the start lowers the chance of rash.

Severe reactions are rare but urgent

Blistering, peeling or sore eyes need emergency care.

Skin and mouth problems are among the reasons people pause or reduce alpelisib, but most can be managed.

Prevention lowers, but does not remove, the risk

Some people still develop rash even with an antihistamine.

Pauses are common

A short break and a lower dose often allow treatment to continue after a rash settles.

Rash can return

Restarting may bring back a rash, so your team watches closely.

What this page cannot tell you

It cannot diagnose a rash from a description. Show your team, or send a photo if they ask for one.

Good mouth care reduces soreness and the risk of infection.

Brush softly

Use a soft toothbrush and mild toothpaste after meals and before bed.

Rinse regularly

Use the mouthwash your team prescribes, or a simple salt-water rinse. Avoid alcohol-based mouthwashes.

Choose soothing foods

Soft, cool, bland foods such as curd rice, khichdi, idli and soups are easier. Avoid very spicy, sour, salty or hot food while sores heal.

See your dentist

Tell your dentist you take alpelisib, and have any dental problems checked early.