Patrick Oconnell
It's a common problem: you take off your shoes at the end of a long day, and they smell like cheese. But why? Well, it's all down to bacteria. Your feet have around 250,000 sweat glands, making them one of the sweatiest parts of your body. When you wear shoes, your feet get warm and moist, and the bacteria on your skin break down the sweat, producing isovaleric acid—the same substance that gives some cheeses their distinctive smell. This process can be exacerbated by wearing synthetic socks, which trap moisture, and by not giving your shoes enough time to dry out between wears.
| Characteristics | Values |
|---|---|
| Number of sweat glands in feet | 250,000 |
| Bacteria responsible for foot odour | Kyetococcus sedentarius, Brevibacterium linens, Brevibacterium aurantiacum |
| Compounds produced by bacteria | Isovaleric acid, Methanethiol, Ammonia |
| Diseases associated with foot odour | Athlete's foot, Bromodosis, Hyperhidrosis |
| Tips to reduce foot odour | Wash feet regularly, wear moisture-wicking socks, wear breathable shoes |
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What You'll Learn
The bacteria Brevibacterium linens is present on human skin and in some cheeses
The bacteria Brevibacterium linens is a gram-positive, rod-shaped bacterium. It is commonly found on human skin and is responsible for foot odour. The distinctive smell is caused by sulfur-containing compounds known as S-methyl thioesters. Interestingly, the same bacterium is also used in the production of certain cheeses, such as Limburger, Munster, and Tilsit cheese, among others.
Brevibacterium linens play a significant role in the fermentation process of these cheeses, contributing to their unique colour, flavour, and aroma. This bacterium is deliberately inoculated onto the surface of smear-ripened cheeses or added to the milk used in the cheese-making process. The presence of B. linens, along with other microorganisms, helps develop the characteristic orange to red colour and pungent smell of these cheeses.
The connection between Brevibacterium linens and the similarity in odour between some cheeses and human feet has even led to scientific discoveries. In 2006, Bart Knols of Wageningen Agricultural University in the Netherlands and his colleagues won the Ig Nobel Prize in biology for their research. They discovered that the female Anopheles gambiae mosquito, a vector of malaria, is equally attracted to the smell of Limburger cheese and human feet.
This finding has practical implications for monitoring and controlling malaria-infested mosquitoes. By using an odour that lures mosquitoes, scientists can design more effective traps to help in the fight against malaria. The research conducted by Dr Knols and his team has received significant recognition and funding to continue their work in reducing the spread of malaria in Africa.
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Sweaty feet are a perfect breeding ground for bacteria
The human foot is home to about 250,000 sweat glands, making it one of the sweatiest parts of the body. Sweat itself is odourless, but when it comes into contact with bacteria, it can produce an unpleasant smell. These bacteria thrive in warm, moist environments, making sweaty feet the perfect breeding ground.
The bacteria responsible for foot odour are typically Brevibacterium linens, which are commonly found on human skin. These bacteria feed on dead skin cells and the salt in sweat, and their waste products contain stinky chemicals also found in skunk spray and rotten eggs. When bacteria break down sweat on the skin, they produce isovaleric acid—the same substance that gives some cheeses their distinctive smell.
Foot odour can be influenced by the type of socks and shoes worn. Synthetic fibres, for example, can trap moisture, creating an ideal environment for bacteria to multiply. In contrast, cotton or wool socks are more absorbent and help keep feet dry. Wearing the same pair of shoes daily prevents them from drying out and turns them into a breeding ground for bacteria. Rotating between different pairs of shoes and choosing well-ventilated options can help reduce foot odour.
While foot odour is usually not a cause for concern, severe sweating and persistent foot odour may indicate a condition called hyperhidrosis. This involves excessive sweating even when an individual is not overheated. Proper foot hygiene, such as regularly washing and thoroughly drying the feet, can help control foot odour. Changing socks daily or more frequently and opting for moisture-wicking socks can also reduce the occurrence of smelly feet.
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Foot odour is usually not a sign of underlying illness
Foot odour, or bromodosis, is a very common condition that is usually not a sign of an underlying illness. It is caused by a build-up of sweat, which results in bacteria growth on the skin. The feet have more sweat glands per square inch than any other area of the body, so it is no surprise that they get sweaty quickly. Additionally, certain foot conditions, such as athlete's foot, may cause smelly feet too.
While foot odour is typically not a cause for concern, there are some cases where it could indicate an underlying health issue. For example, severe sweating and foot odour throughout all seasons could be a sign of hyperhidrosis, which is excessive sweating even when one is not overheated. People with diabetes may also experience foot odour and need to take special care of their feet as they are more prone to developing corns and calluses, as well as peripheral neuropathy and peripheral artery disease, which can lead to foot damage.
In most cases, however, foot odour can be easily remedied with proper foot care and hygiene. It is important to wash and dry the feet thoroughly, especially between the toes, where bacteria can easily grow. Keeping toenails short and clean, using foot files to remove hard skin, and wearing clean socks can also help reduce foot odour.
While foot odour is typically not a medical concern, it can be embarrassing and uncomfortable for those who experience it. Home treatments and over-the-counter products are usually effective in reducing or eliminating foot odour. However, if home remedies do not help, it is recommended to consult a doctor or a foot specialist (podiatrist) for stronger treatments or medical advice.
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The type of socks you wear can make a difference
Secondly, the material of your socks can make a difference. You should opt for socks that absorb moisture rather than synthetic socks that keep it on your feet. Thick, soft socks made out of natural fibres are a good option, as are sports socks.
Thirdly, it is important to ensure your socks are clean. Bacteria can collect on your socks, so it is important to wash them regularly.
Finally, you should consider alternating between two pairs of shoes, so that they have time to dry out from sweat or moisture.
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Limburger cheese is used to lure mosquitoes into traps
The reason Limburger cheese is used is that it is cultured with Brevibacterium epidermidis, a bacterium found on human skin. This is the same bacterium that causes foot odour, which is why people's feet can sometimes smell like cheese. Up to 15% of people have very smelly feet due to the type of bacteria that grows (Kyetococcus sedentarius). While foot odour is usually not a sign of any underlying health issues, it can be a cause for concern for people with diabetes, who need to take special care of their feet.
The discovery that mosquitoes are attracted to the same odour that Limburger cheese produces has led to the development of odour-baited traps for mosquito surveillance and control. These traps are likely to become an important tool in monitoring and controlling the spread of mosquito-borne diseases, especially in regions like sub-Saharan Africa, where malaria is prevalent.
The use of Limburger cheese in mosquito traps is a creative and innovative solution to a significant global health problem. By exploiting the connection between mosquito attraction to human odour and the odour emitted by Limburger cheese, scientists have developed a simple yet effective tool with the potential to save lives.
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Frequently asked questions
The primary cause of foot odour is bacteria breaking down sweat on the skin, producing a cheese-like smell due to isovaleric acid.
Washing your feet regularly and drying them thoroughly can help. It is also recommended to change socks daily and opt for moisture-wicking socks and breathable shoes.
Synthetic fibres can trap moisture, creating an inviting environment for bacteria. Cotton or wool socks are better at absorbing sweat and keeping your feet dry.
While foot odour is usually not a sign of an underlying illness, severe sweating and foot odour throughout the year could indicate hyperhidrosis, a condition characterised by excessive sweating.
Interestingly, yes! The same bacteria that cause foot odour, Brevibacterium linens, are also found on certain cheeses like Limburger. This knowledge has led to experiments using Limburger cheese to lure mosquitoes into traps, aiding in the fight against malaria.
