TL;DR
A bike helmet is cleaned with mild soap and cool water and nothing stronger, because solvents and heat degrade the protective foam invisibly. Wash the removable pads and straps by hand, wipe the shell, and air dry away from direct sun. A helmet that has taken an impact is replaced, not cleaned back into service.
The rule that matters more than the smell
Everything below is about a helmet that is still safe to wear. Before any of it, understand the one thing a cleaning routine cannot fix.
A bike helmet protects your head by crushing. The expanded polystyrene foam inside is designed to compress in a crash and absorb energy that would otherwise reach your skull. Once it has compressed, it does not spring back.
That means a helmet is replaced after any impact, even one that leaves no visible mark, and even if it was only dropped hard onto pavement. The damage can be an internal crush zone you cannot see.
It also means solvents are off the table. Many common solvents and strong cleaners attack polystyrene foam and the adhesives holding the shell to it. The damage does not show. The helmet looks fine and no longer performs.
Source: Consumer Product Safety Commission bicycle helmet standard and manufacturer replacement guidance
How do you clean a bike helmet?
Remove the pads and wash them by hand in cool water with a small amount of mild soap or gentle detergent. Wipe the outer shell and the inner foam with a cloth dampened in the same solution, rinse with a clean damp cloth, and air dry everything completely away from heat and sun.
What you may use, and what you may not
Use: mild dish soap, baby shampoo, or a gentle laundry detergent, in cool or lukewarm water. A soft cloth. A soft brush for vents. Plain water for rinsing.
Do not use: solvents of any kind, degreaser, rubbing alcohol, acetone, bleach, ammonia-based glass cleaner, abrasive cleaners, or scouring pads. Do not put a helmet in a dishwasher, a washing machine, or a clothes dryer. Do not leave it on a heater, in a hot car, or in direct sun to dry.
Heat is as damaging as solvent. Polystyrene starts to soften and deform well below the temperature inside a parked car on a warm day.
Whatever the manufacturer printed inside your helmet or on its manual overrides anything here. If the manual names a specific product or forbids one, follow it.
The step-by-step
1. Take the pads out. Most modern helmets have hook-and-loop pads that lift straight out. Note where each one sits before you remove them all.
2. Hand wash the pads. Cool water, a drop of mild soap, squeeze gently rather than wringing. Wringing crushes the foam padding and it will not recover its shape. Rinse until the water runs clear.
3. Wash the straps in place. Dampen a cloth with the soapy water and work along the webbing. Salt from sweat is what makes straps stiff and smelly. Rinse the same way with a clean damp cloth.
4. Wipe the shell. The hard outer shell tolerates mild soap and water well. A soft brush clears bugs and road grit out of the vents.
5. Wipe the inner foam gently. Damp cloth only. Do not soak the foam, do not scrub it, and do not pick at it.
6. Air dry completely. Somewhere with airflow, out of the sun, at room temperature. Pads dry flat. Reinstall the pads only when both they and the helmet are fully dry.
Why does my helmet smell?
Sweat soaks into the pads and straps, and the salts and skin oils in it feed odor-causing bacteria as the helmet sits in a warm bag or a closed garage. Washing the pads and straps removes the food source. Drying the helmet fully after every ride prevents most of it.
Keeping a helmet from getting bad in the first place
Rinse or wipe the pads after hot rides rather than waiting for a smell.
Do not store a helmet in a sealed bag, in a car, or hanging in direct sun. Heat is the enemy twice over: it degrades the foam and it bakes sweat into the padding.
Let it air out after every ride. A hook in a ventilated spot beats a closet, and the same drying-first principle applies to the rest of the bike in how to wash a bike frame without damage.
Replacement pad sets are available for many helmets and cost far less than a new helmet. Once pads have gone hard, thin, or permanently smelly, swapping them is the fix.
When does a helmet get replaced?
Immediately after any crash or hard impact, regardless of how it looks. Also when the shell is cracked, the foam is dented or crumbling, the straps are frayed, the buckle does not hold, or the fit system has broken. Many manufacturers also suggest replacement after roughly five years of use.
The five-year figure is not about dirt. It reflects gradual degradation of the foam and straps from sweat, ultraviolet light, and temperature swings.
A helmet bought secondhand has an unknown impact history, which is why safety organizations advise against it.
Kids helmets specifically
Children's helmets get more sweat, more dirt, and more drops than adult ones.
Check them often. Kids will not report that a helmet hit the driveway. Look for cracks in the shell, dents in the foam, and a fit system that no longer clicks tight.
Fit changes as a child grows, and a loose helmet does not protect. The same weekly check that covers a kids bike in cleaning a kids bike and scooter is a good time to look the helmet over.
The same rule applies to other safety gear
Load-bearing protective equipment is not a cleaning problem, it is a replacement decision.
Climbing helmets, ski and snowboard helmets, motorcycle helmets, and hard hats all share the logic: mild soap and water only, follow the manufacturer's instructions, and retire the item after an impact rather than trying to restore it.
Body armor, pads, and harnesses have their own manufacturer rules, and solvents ruin most of them. Our guide to cleaning outdoor gear and equipment covers the softer gear that shares a closet with it.
FAQ
Can you put a bike helmet in the washing machine?
No. Machine agitation crushes the protective foam and can separate the shell from the liner, and machine heat softens polystyrene. Remove the pads and hand wash them in cool water with mild soap, then wipe the shell and inner foam with a damp cloth and air dry everything.
What can I use to get the smell out of a bike helmet?
Mild soap and cool water on the pads and straps, since sweat salts in the padding are the source. Rinse well and dry fully with airflow. Avoid alcohol, solvents, and strong disinfectants, which damage the foam. If the smell persists, replacement pad sets are available for most helmets.
Does a helmet need replacing after being dropped?
A drop from a bike rack or a table onto pavement usually does not compromise a helmet, but a hard impact does, and the crush damage is often invisible. If the helmet took a real hit or was worn in a crash, replace it. When in doubt, contact the manufacturer, since many offer crash-replacement programs.
Can I use disinfecting wipes on my helmet?
Check what is in them first. Wipes containing alcohol, bleach, or strong solvents can degrade the foam liner and the adhesives. Mild soap and water is the safe default. If your helmet manual names an approved product, follow the manual over any general advice.
How often should you clean a bike helmet?
Wash the pads every few rides in warm weather and monthly with light use, and wipe the shell whenever it gets dirty. Airing the helmet out after every ride does more for odor than deep cleaning does. Sweat that never dries is what causes most helmet smell.
How long does a bike helmet last?
Many manufacturers suggest replacing a helmet after about five years, because foam, straps, and adhesives degrade with sweat, sunlight, and heat over time. Replace sooner if the helmet has taken an impact, the shell is cracked, the foam is dented, or the straps or buckle no longer hold securely.
Gear that lives in a garage tends to bring the garage into the house. If keeping up with the rest of it is the harder job, get a quote or read more about house cleaning services.