What You Should Know About Xolair Side Effects

Xolair (Omalizumab) is a biologic medication used to treat severe allergic asthma, chronic hives, nasal polyps, and food allergies. Like all medications, it comes with potential side effects — some mild and manageable, others that need immediate medical attention.

This guide breaks down the most common and serious side effects of Xolair so you know exactly what to expect and when to call your doctor.

Common Side Effects of Xolair

Most people who take Xolair experience mild side effects, especially during the first few months of treatment. These usually improve over time:

Injection Site Reactions

The most common side effect. You may notice:

• Pain or soreness at the injection site
• Redness or swelling
• Itching or warmth
• Bruising

These reactions are usually mild and go away within a few hours to a few days. Applying a cold compress can help reduce discomfort.

Other Common Side Effects

• Headache — Reported by many patients, especially early in treatment
• Joint pain (arthralgia) — Mild aching in joints
• Fatigue — Feeling tired or low-energy after injections
• Dizziness — Usually mild and temporary
• Upper respiratory infections — Cold-like symptoms including sore throat and runny nose
• Ear pain — More common in younger patients
• Nausea — Typically mild
• Nosebleeds — Occasional and usually not serious

Most of these side effects are mild and don't require you to stop treatment. However, always mention them to your doctor at your next visit so they can track how you're responding.

Serious Side Effects of Xolair

While uncommon, Xolair can cause serious side effects that need immediate medical attention. Understanding these is critical for your safety.

Anaphylaxis (Boxed Warning)

This is the most important side effect to know about. Xolair carries an FDA boxed warning for anaphylaxis — the most severe type of allergic reaction.

Key facts about anaphylaxis with Xolair:

• It can happen after any dose, not just the first one
• It can be delayed — occurring hours or even days after your injection
• Symptoms include difficulty breathing, swelling of the face/throat, rapid heartbeat, dizziness, and hives
• This is why your first injections must be given in a healthcare setting with monitoring

What to do: If you experience any signs of anaphylaxis, use your injectable epinephrine (EpiPen) immediately and call 911. You should always carry epinephrine while on Xolair.

Serum Sickness-Like Reactions

Some patients develop symptoms 1 to 5 days after an injection:

• Fever
• Muscle and joint aches
• Rash
• Swollen lymph nodes

Contact your doctor right away if you develop these symptoms after a Xolair injection.

Eosinophilic Conditions

In rare cases, Xolair has been associated with eosinophilic conditions, including Churg-Strauss syndrome (a type of blood vessel inflammation). Symptoms may include:

• Worsening breathing problems
• Numbness or tingling in the hands or feet
• Rash
• Flu-like symptoms

This is more likely to occur when corticosteroid doses are being tapered. Never stop corticosteroids suddenly — always taper under your doctor's guidance.

Increased Cancer Risk

Clinical trials showed a slightly higher rate of cancer in patients taking Xolair compared to those not taking it. The connection is not fully understood, and it's unclear whether Xolair directly causes cancer. Discuss your personal risk factors with your doctor.

Parasitic Infections

Because Xolair affects the immune system's IgE response (which also helps fight parasites), patients may be at higher risk for parasitic infections. This is especially relevant if you:

• Travel to areas where parasitic infections are common
• Live in tropical or subtropical regions

Tell your doctor if you're planning international travel.

Cardiovascular Events

Some studies have noted heart attacks, blood clots, and strokes in Xolair patients, though a direct causal link has not been established. If you have existing heart disease risk factors, discuss them with your doctor.

Side Effects by Condition

Your experience with side effects may vary depending on why you're taking Xolair:

Asthma Patients

The most commonly reported side effects in asthma trials were injection site reactions, viral infections, upper respiratory infections, sinusitis, headache, and sore throat.

Chronic Hives (CSU) Patients

In CSU trials, the most common side effects were headache, injection site reactions, and upper respiratory infections. Nausea and joint pain were also reported.

Food Allergy Patients

Since the food allergy indication is relatively new (approved February 2024), long-term side effect data is still being collected. The most common reported side effects are similar — injection site reactions and respiratory infections.

When to Call Your Doctor

Contact your doctor if you experience:

• Side effects that don't go away or get worse over time
• Fever, rash, or joint pain 1-5 days after injection
• Worsening breathing problems, especially if you're tapering corticosteroids
• Signs of infection that won't clear up
• Any new or unusual symptoms after starting Xolair

Call 911 or use your EpiPen immediately if you experience:

• Difficulty breathing or swallowing
• Swelling of your face, lips, tongue, or throat
• Severe dizziness or fainting
• Rapid or weak pulse
• Widespread hives or skin flushing

Tips for Managing Side Effects

• Stay at the clinic for the recommended observation period after each injection
• Always carry epinephrine — your doctor will prescribe this when you start Xolair
• Keep a symptom journal — track any side effects and when they occur so you can share details with your doctor
• Don't skip appointments — regular check-ins help your doctor monitor for serious reactions
• Ice the injection site — a cold compress before and after can reduce pain and swelling

Final Thoughts

Most Xolair patients tolerate the medication well, and the benefits for conditions like severe asthma, chronic hives, and food allergies can be life-changing. The key is knowing what to watch for and having a plan in place for serious reactions.

If you're considering Xolair, learn more about what Xolair is and how it's used, or read about how Xolair works at a deeper level. If cost is a concern, check out our guide on saving money on Xolair.