Foot odor is a part of body odor that affects a person’s feet and is usually an unpleasant odor. Body odor originates from the whole body, such as sweat, sebaceous glands, senile glands, as well as bad breath, bad hair, and bad feet, and originates from a localized part of the body. Therefore, finding the main component of body odor in each area and finding the mechanism that produces body odor is beneficial to help control body odor. For example, the main components of hair odor are short-chain fatty acids and aldehydes, which are produced by normal flora with strong esterase activity such as Staphylococcus scalpis and Malassezia furfur breaking down sebum secreted by the scalp. Cause: The main cause of foot odor is foot sweat. Sweat itself is odorless, but provides a breeding ground for certain bacteria that produce some unpleasant smelly substances. These bacteria are naturally present on our skin, part of the natural human flora. The front part of the foot produces the most sweat. Therefore, some factors that cause excessive sweating, such as wearing non-breathable shoes for long periods of time, can cause excessive local sweating. Socks themselves do not usually cause foot odor, but when wearing shoes, socks tend to capture the hairs on the feet, especially on the toes, which can increase the surface area for bacterial growth, thus leading to aggravated foot odor. If socks are in direct contact with the feet, the composition of the socks has an effect on foot odor. Polyester and nylon socks are common industrial synthetic socks. Wearing polyester or nylon socks can increase sweating because they are not as breathable as cotton socks, which can aggravate foot odor. Socks help absorb sweat, and shoes are not washed as often as socks. If you don’t wear socks, sweat tends to collect in your shoes and bacteria grow over time. Closed shoes do have enough air circulation and thus help bacteria grow, especially at the toes where sweat is most abundant, sweat cannot evaporate, and there are no socks to absorb sweat. Over time, dead skin, dirt, oil can likewise gather inside the shoes, leading to increased foot odor. If you do not wear socks, fungus or mold also tend to breed, thus aggravating foot odor. If closed shoes (such as flats or high heels) cannot be worn with socks, the best way is not to take off your shoes when your feet start to feel hot or sweaty, thus allowing the sweat on your shoes and feet to evaporate. Foot powder can reduce moisture and odor. Mechanism of odor origin: Odor is often described as a thick cheese smell. Some people describe it as some kind of malt vinegar smell. Sometimes, it can also be an ammonia-like odor. The genus Staphylococcus is the main cause of foot odor because this bacterium digests the dead skin on the feet and converts methionine into methionine, a colorless gas containing sulfur aromatics with a peculiar putrid odor. Dead skin is common on the soles of the feet and in the toe joints. Propionic acid is also present in many foot sweats. This propionic acid is a metabolite of the breakdown of amino acids by Propionibacterium. Propionibacterium is present in the sebaceous glands of adolescents and adults. Propionic acid is chemically similar to acetic acid and is a colorless liquid with a vinegar-like odor. Isovaleric acid, another source of foot odor, is produced by Staphylococcus epidermidis breaking down leucine in sweat and can cause intense cheese-like foot odor. Some other microorganisms such as Micrococcaceae, Corynebacterium, and S. furfuraceum spp. are also involved in the formation of foot odor. Bacillus subtilis can also cause strong foot odor. Odor removal: Aromatic deodorants can be used to neutralize foot odor or absorb foot odor, such as activated charcoal insoles. Antiperspirants containing urotropine can be effective in removing foot odor. Some natural substances and aromatics can inhibit the growth of bacteria that produce foot odor without disrupting the normal flora. Citral, citronellal, and geraniol can all reduce the concentration of isovaleric acid, thereby reducing foot odor.