Randy Chandler
The idea that Americans smell like cheese is a stereotype with unclear origins. However, body odour is influenced by a variety of factors, including diet, hygiene, genetics, and the bacteria on the skin. While diet and hygiene are the main causes of body odour, genetics also play a role, and the bacteria found in the armpits of men contribute to a cheese-like smell.
| Characteristics | Values |
|---|---|
| Reason for the smell | Bacteria on the skin metabolize the compounds that come out of sweat glands |
| Type of sweat gland | Eccrine glands and apocrine glands |
| Bacteria | Corynebacterium, Staphylococcus haemolyticus, Staphylococcus hominis, Staphylococcus epidermidis, Propionibacteria |
| Bacteria population | Greater population of Corynebacterium jeikeium found in men's armpits; greater population of Staphylococcus haemolyticus found in women's armpits |
| Compounds | Lipases, butyric acid, propionic acid, isovaleric acid, thioalcohol compounds |
| Diet | Garlic, onions, spicy foods, meat, eggs, cheese, soy, refined carbohydrates, fruits, and vegetables |
| Hygiene | Showering, use of deodorant, antiperspirants, and prescription antiperspirants |
| Genetics | Genetic makeup |
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What You'll Learn
The role of bacteria in body odour
Body odour, or body odour (BO), is present in all humans and its intensity can be influenced by several factors, including behavioural patterns, survival strategies, sex, diet, health, medication, and hygiene practices. The major contribution to body odour comes from bacterial activity on skin gland secretions.
Body odour is primarily caused by apocrine sweat glands, which become activated during puberty. These glands develop in hairy regions like the armpits, genitals, and scalp, where they secrete an oily fluid comprised of proteins, lipids, and steroids. This fluid is naturally almost entirely odourless. It is only when members of the skin microbiota metabolize these secretions that they produce the malodorous byproducts that cause body odour. In humans, the armpits offer a moist, warm environment where microbes can thrive, making them a microbial hotspot. The composition of the skin microbiota varies from one individual to another and even between locations on the same person. However, the major bacterial players that colonize the skin and produce body odour are similar. Some common skin bacteria that produce body odour include members of the Corynebacterium, Staphylococcus, and Cutibacterium genera.
The biochemistry behind the microbial conversion of sweat to malodorous products is not yet fully understood. However, the odour can be largely attributed to the production of volatile organic compounds (VOCs), including volatile fatty acids and thioalcohols. Key volatile fatty acids that contribute to body odour include 3-methyl-2-hexenoic acid (3M2H), which has a 'goat-like' odour, and 3-hydroxy-3-methylhexanoic acid (HMHA), which has a 'cumin-like' odour. These odorants are produced by some members of Corynebacterium. Other medium- and short-chain fatty acids also contribute to odour. For example, isovaleric acid, a compound produced by Staphylococcus epidermis, has a cheesy-smelling odour.
The body odour of human males plays an important role in human sexual attraction, as a powerful indicator of MHC/HLA heterozygosity. Research suggests that women are attracted to men whose body odour is different from theirs, indicating that they have immune genes that are different from their own, which may produce healthier offspring. The ABCC11 gene is also linked to body odour, as it encodes a protein that transports molecules across cellular membranes, including molecules in the sweat. If the ABCC11 gene is non-functional, the sweat molecules cannot cross the membrane barrier to reach the armpit, and the bacteria on the other side of the skin surface are unable to access or metabolize the organic compounds in the sweat, resulting in a decrease in body odour.
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Diet and body odour
Dr Constantine George, an internal medicine specialist, explains that sweat itself does not have a smell. However, when it comes into contact with the bacteria on our skin, it can produce its own odour. This is why people who are exposed to the same bacteria, such as family members or people living in the same household, may share a common smell.
The types of bacteria on our skin can also influence the way we smell. For example, men tend to have higher levels of an odourless fatty acid, which, when mixed with armpit bacteria, can produce a cheese-like smell. On the other hand, women's sweat contains higher levels of a sulfur-containing compound, which, combined with bacteria, produces a chemical called thiol, known for smelling like onions.
What we eat can also have an impact on our body odour. For instance, eating garlic or onions can cause compounds to be released through the pores of the skin, resulting in an unpleasant odour. Similarly, a diet high in refined carbohydrates can lead to a less appealing body odour, while a diet rich in fruits and vegetables is associated with a more attractive smell.
In addition to diet, other factors such as genetics, age, and sexual life can also influence body odour. Body odour can even be an indicator of certain diseases, such as diabetes or kidney disease.
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Genetics and body odour
Body odour, or BO, is influenced by many factors, including genetics, sex, diet, health, medication, and personal hygiene. It is present in all animals and can serve an important survival function. For example, a strong body odour can signal a warning to predators or indicate that the prey animal is unpalatable.
Body odour is caused by bacterial activity on skin gland secretions. Humans have three types of sweat glands: eccrine sweat glands, apocrine sweat glands, and sebaceous glands. While eccrine sweat glands are present in all skin types, apocrine and sebaceous glands are restricted to certain areas of the body, such as the armpits, genitals, and scalp. These areas provide a warm and moist environment where microbes can thrive, making them hotspots for body odour. The composition of skin microbiota varies between individuals and even between different locations on the same person. However, certain bacteria, such as those from the Corynebacterium, Staphylococcus, and Cutibacterium genera, are commonly associated with body odour. These bacteria metabolize the secretions from sweat glands, producing malodorous byproducts, including volatile fatty acids and thioalcohols, which contribute to body odour.
Genetics plays a significant role in body odour, with research suggesting that it can influence whether an individual's sweat contains compounds that bacteria can metabolize, leading to armpit odour. The ABCC11 gene, for instance, has been identified as directly responsible for underarm odour. Individuals with a non-functional ABCC11 gene lack the chemical needed by the bacteria that cause underarm odour, resulting in reduced or no underarm odour. This loss-of-function mutation is common in East Asian populations. Additionally, the OR7D4 gene has been found to influence how individuals interpret certain scents, with variations in this gene impacting the perception of odourant molecules.
Beyond the influence of genetics, an individual's diet can also impact their body odour. For example, the consumption of certain foods and drinks can affect body odour, and in the case of Americans, a diet rich in dairy products, as exemplified by the "milk in the fridge" stereotype, could potentially contribute to the perception of a cheese-like body odour. However, it is important to note that body odour is a complex interplay of various factors, and other aspects such as personal hygiene and hormones also come into play.
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Hygiene and body odour
Body odour is influenced by the actions of the skin flora, including members of Corynebacterium, which manufacture enzymes that break down the lipids in sweat to create smaller molecules like butyric acid. Greater bacteria populations of Corynebacterium jeikeium are found more in the armpits of men, whereas greater population numbers of Staphylococcus haemolyticus are found in the armpits of women. This causes male armpits to give off a rancid, cheese-like smell, whereas female armpits give off a more fruity, onion-like smell. Staphylococcus hominis is also known for producing thioalcohol compounds that contribute to body odours.
Body odour is created when the bacteria on our skin metabolise the compounds that come out of our sweat glands. Eccrine glands are the most common and can be found throughout the body, secreting sweat directly onto the skin. Apocrine glands can be found in areas like the armpits and groin, and dump their sweat into hair follicles first. While these glands create sweat that mixes with bacteria to make us smelly, they also control our body temperature.
Factors such as food, drink, gut microbiome, genetics, sexual life, age, and hygiene can affect body odour. For example, eating garlic, onions, and spicy foods can cause compounds to be produced and released through the pores of the skin, making you smell like body odour. A 2006 study found that women preferred the odour of men who ate a non-meat diet, including more eggs, cheese, soy, fruits, and vegetables.
To improve hygiene and reduce body odour, it is recommended to shower at least once a day, or maybe twice. When lathering up, avoid soaps heavy on chemicals, dyes, and fragrances. After showering, Americans in particular might consider rubbing on deodorant under the arms, as 90% of Americans and 92% of teenagers use antiperspirants or deodorants.
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The perception of body odour
Body odour, or bromhidrosis, is caused by bacteria on the skin metabolising the compounds that come out of our sweat glands. While sweat itself is odourless, it is the bacteria that produce the smell. The human body has two types of sweat glands: eccrine glands, which are found all over the body and secrete sweat directly onto the skin, and apocrine glands, which are found in areas like the armpits and groin and release sweat into hair follicles.
Hygiene is another critical factor in the perception of body odour. Inadequate hygiene can lead to an overgrowth of bacteria on the skin, resulting in a stronger odour. This is particularly true in areas with a high concentration of sweat glands, such as the armpits. Maintaining proper hygiene, including showering regularly and using deodorant or antiperspirant, can help mitigate body odour.
It is worth noting that body odour can also be an indicator of health and disease. For instance, an unusually fruity or sweet body odour may be a sign of diabetes, while an ammonia smell in the body, urine, or breath could indicate kidney disease. Additionally, stress can also influence body odour, as stressful situations can trigger a cascade of reactions in the brain, leading to the production of certain odours.
While the perception of body odour may vary among individuals, it is clear that a combination of factors, including diet, hygiene, genetics, and health, contribute to the unique scent of each person.
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Frequently asked questions
There could be several reasons why Americans are perceived to smell like cheese. Firstly, diet plays a significant role in body odor, and certain foods like cheese, eggs, soy, fruits, and vegetables can influence the way someone smells. Additionally, Americans are known for their love of dairy products, which may contribute to the stereotype.
The bacteria on our skin metabolize the compounds that come out of our sweat glands, resulting in body odor. Therefore, what we eat can indirectly affect the way we smell.
Apart from diet, factors such as genetics, age, sexual life, and hygiene can also impact body odor. Additionally, certain medical conditions and medications can alter the way someone smells.
Yes, there is a perception of Americans as consuming large quantities of dairy products, including milk and cheese. This perception may contribute to the stereotype of Americans smelling like cheese.
Maintaining good hygiene practices, such as showering daily and using deodorant or antiperspirant, can help reduce body odor. Additionally, being mindful of dietary choices and avoiding excessive sweating can also minimize odor.
