Hot tubs provide a convenient way to unwind and loosen weary muscles. But a dirty-sock smell can stop that relaxation before it even begins. Like swimming pools, hot tubs require special maintenance and chemicals to keep the water clean and safe. Stay on top of routine maintenance and track down the source of any foul odors as soon as the smell is noticed.
A dirty sock smell in a hot tub can be caused by mold or mildew in and around the hot tub. Mold and mildew are types of fungi that grow in hot, humid and moist conditions. They can have a musty, dirty smell that is very strong, especially if the cover has been only recently removed from the hot tub. Allow your hot tub to fully air out for up to 10 minutes after you remove the cover. If the smell persists, there may be mold or mildew around the hot tub on grout, tiles, the walls or other nearby areas. These should be cleaned with a bleach solution to remove the smell, but the bleach should be tested on a small, hidden area of the hot tub beforehand to ensure it will not damage the finish or color.
Most hot tub covers are made of foam that is covered in a vinyl or plastic material. The vinyl and plastic are waterproof, but tiny tears or holes in this lining can expose the foam inside to moisture, causing mold or mildew problems. If the cover itself is the source of the dirty sock smell, it will need to be replaced.
Different species of algae can have varying smells, from musty and dirty sock-like to rotten egg or sulfur smells. Algae grows in swimming pools and hot tubs even with the presence of some chemicals used to keep the water clean, such as chlorine. Visible algae should be scrubbed off of the hot tub surfaces with a stuff brush, and an algicide can be used to kill the algae and keep it from returning.
Hot tub owners who don't shower before getting into the hot tub can bring bacteria with them. This bacteria is usually killed by chemicals in the water, but an excess amount of bacteria can become trapped in the air between the cover and the water's surface. This bacteria can emit a dirty sock odor, which will dissipate once the cover is removed and the hot tub is allowed to air out for 10 to 15 minutes before use.
Hot tub owners can choose between using chlorine and bromine to disinfect the hot tub. These chemicals kill bacteria and prevent mold growth, but bromine can have a musty smell that is similar to dirty socks.