Do Fasenra or Nucala Protect Against Wildfire Smoke?

If you have severe eosinophilic asthma (SEA), taking an anti-IL-5 biologic like Fasenra (benralizumab) or Nucala (mepolizumab) can provide a layer of protection against the effects of wildfire smoke, but it does not make your lungs immune to smoke damage. Studies show that patients with severe asthma who are on biologic therapies have a reduced risk of experiencing persistent asthma symptoms following intense smoke exposure compared to those who are not on these medications ^[1][2].

By keeping your baseline asthma well-controlled and reducing underlying inflammation, these medications make your airways less reactive to environmental triggers ^[3][4]. However, wildfire smoke contains fine particulate matter (PM2.5) that triggers multiple types of lung irritation, some of which are not blocked by your biologic ^[5][6].

How Your Biologic Helps During Smoke Events

Fasenra and Nucala work by targeting and depleting eosinophils—a specific type of white blood cell that causes swelling and inflammation in your airways ^[7][8]. When your eosinophil levels are kept low by these medications:

• Lower Baseline Inflammation: Your lungs are calmer day-to-day. When smoke enters your airways, it is hitting lungs that have lower airway hyperresponsiveness (meaning they are less “twitchy”), so the smoke is less likely to trigger an immediate, severe attack ^[3][9].
• Fewer Severe Exacerbations: These medications are proven to significantly reduce the overall frequency of severe asthma attacks ^[10][11].
• Quicker Recovery: Because your baseline inflammation is managed, research suggests you may recover faster and have fewer lingering symptoms after the smoke clears ^[1].

Why You Still Need to Protect Yourself

While your biologic protects you against eosinophil-driven inflammation, wildfire smoke is a complex mix of toxic gases and fine particles (PM2.5). When you breathe in wildfire smoke, it triggers different types of reactions in your lungs that Fasenra and Nucala do not treat:

• Direct Irritation and Toxicity: The physical particles in smoke act like sandpaper in your airways, causing direct physical irritation, general inflammation, and oxidative stress (a type of chemical damage to your lung cells) ^[6][12].
• Neutrophilic Inflammation: Smoke often causes your body to deploy a different type of immune cell called neutrophils to clean up the ash and debris ^[13]. Because your biologic only targets eosinophils, it cannot stop this neutrophil-driven inflammation.
• Increased Infection Risk: Heavy smoke exposure can impair your immune system’s ability to fight off bacteria and viruses, leaving you vulnerable to secondary respiratory infections ^[13].

Action Steps During Wildfire Season

Even if your asthma feels completely controlled on Fasenra or Nucala, you must treat wildfire smoke as a serious threat.

• Track Air Quality Carefully: Monitor local Air Quality Index (AQI) forecasts, paying special attention to PM2.5 levels. Because you have severe asthma, you should consider staying indoors when the AQI reaches 100 (“Unhealthy for Sensitive Groups”), or even sooner if you notice symptoms.
• Create a Clean Air Sanctuary: Keep windows closed and use HEPA air purifiers to keep indoor air clean. If you have a central HVAC system, check if you can upgrade to MERV-13 filters, which are highly effective at trapping PM2.5 particles.
• Wear a High-Quality, Tight-Fitting Mask: If you must go outside, wear an N95 or KN95 respirator mask. The mask must fit tightly against your face without gaps—a loose mask will let fine smoke particles slip right through.
• Review Your Asthma Action Plan: Before smoke season begins, review your written asthma action plan with your doctor. Know exactly what steps to take if the smoke triggers an attack.
• Know When to Seek Emergency Care: Keep your rescue inhaler (albuterol) handy. If you use your rescue medication and it does not provide relief, or if you experience rapidly worsening shortness of breath, severe chest tightness, or trouble speaking in full sentences, follow your action plan and seek immediate emergency medical attention.