An asthma inhaler contains a small dose of medication, a propellant to push it into your lungs, and sometimes a carrier substance or co-solvent to keep the formulation stable. The exact ingredients depend on whether you’re using a quick-relief (rescue) inhaler or a daily maintenance inhaler, and whether it comes as a pressurized spray or a dry powder.
What’s in a Rescue Inhaler
The most common rescue inhaler contains albuterol (called salbutamol outside the U.S.). Each puff delivers about 90 micrograms of the active drug. That’s a tiny amount, roughly one ten-thousandth of a gram, but it’s enough to relax the muscles wrapped around your airways within minutes. A standard canister holds 200 metered doses.
Albuterol works by binding to receptors on the smooth muscle cells lining your airways. When those receptors are activated, calcium levels inside the muscle cells drop, and the muscles stop contracting. The result is that narrowed airways open back up, and breathing gets easier. This effect kicks in within about five minutes and lasts roughly four to six hours.
What’s in a Maintenance Inhaler
Daily-use inhalers typically contain a corticosteroid, which works differently from a rescue inhaler. Instead of relaxing muscles, it dials down inflammation. The steroid molecule passes into airway cells and essentially switches off the genes responsible for producing inflammatory proteins. Over days and weeks, this reduces the chronic swelling that makes asthma airways so reactive in the first place. Widely used corticosteroids for inhalers include budesonide, fluticasone, beclomethasone, and mometasone.
Some maintenance inhalers combine a corticosteroid with a long-acting bronchodilator. Where albuterol opens airways for a few hours, long-acting versions of the same type of drug keep airways relaxed for 12 to 24 hours. These combination inhalers give you both anti-inflammatory and airway-opening benefits in a single device. Triple-therapy inhalers go a step further, adding a second type of long-acting bronchodilator that works through a completely different pathway, blocking the nerve signals that tell airway muscles to tighten.
The Propellant
If your inhaler is the pressurized spray type (a metered-dose inhaler, or MDI), the bulk of what’s in the canister is actually propellant, not medication. Current inhalers use hydrofluoroalkane (HFA) propellants. These replaced the older chlorofluorocarbon (CFC) propellants that damaged the ozone layer.
HFA propellants are considered safe to inhale, but they do contribute to greenhouse gas emissions. Newer propellants with a much lower climate impact are in development. One candidate, HFC-152a, has a global warming potential about 90% lower than current HFA propellants. These alternatives are still working through safety testing and may not reach the market for a few years, though regulatory pressure in both the EU and the U.S. is pushing the transition forward. Under the American Innovation and Manufacturing Act, the current HFA propellants will be phased down by 2030 at the latest.
Co-Solvents and Stabilizers
Many metered-dose inhalers also contain a small amount of ethanol as a co-solvent. Ethanol helps dissolve the medication evenly in the propellant so each puff delivers a consistent dose. Formulations typically use between 10% and 20% ethanol by weight. At those concentrations, the actual amount of ethanol per puff is minuscule, far less than what you’d find in a drop of mouthwash.
Some formulations include tiny amounts of other stabilizers, such as oleic acid or dilute acid solutions, to keep the drug particles from clumping or sticking to the inside of the canister. These are listed as inactive ingredients on the packaging.
What’s Different in Dry Powder Inhalers
Dry powder inhalers (DPIs) skip the propellant entirely. Instead, you inhale the medication as a fine powder, using your own breath to pull it into your lungs. The active drug particles are extremely small, between 1 and 5 micrometers in diameter, so they can travel deep into the airways.
Because these particles are so tiny, they’d be nearly impossible to handle on their own. So DPI formulations mix the drug with larger carrier particles, most commonly lactose. Alpha-lactose monohydrate is the standard carrier approved for inhalation products. Glucose and mannitol are also FDA-approved alternatives, though lactose dominates because of its stability, safety record, and low cost. When you inhale, the drug particles separate from the lactose carriers and travel into your lungs while the larger lactose particles deposit harmlessly in your mouth and throat. If you have a severe milk allergy, the trace milk proteins that can remain in pharmaceutical-grade lactose are worth discussing with your prescriber.
How Much Actually Reaches Your Lungs
No inhaler delivers 100% of its medication to the lungs. A significant portion lands in the mouth, throat, or is exhaled. Metered-dose inhalers deposit roughly 8% to 53% of the drug in the lungs, a wide range that depends heavily on your technique. Dry powder inhalers average around 20%, though the range extends higher with newer designs. Soft mist inhalers, a newer device type that creates a slow-moving aerosol cloud, achieve some of the best lung deposition rates at 39% to 67%.
This is why technique matters so much. The same inhaler with the same ingredients can deliver dramatically different doses depending on how you use it. Spacer devices, which attach to metered-dose inhalers, help by slowing the aerosol and giving you more time to inhale it, pushing delivery toward the higher end of those ranges. Whatever device you use, the medication that doesn’t reach the lungs is mostly swallowed or exhaled, which is one reason inhaled corticosteroids are designed to be poorly absorbed through the gut, minimizing side effects from the portion you accidentally swallow.