Why Koreans, Chinese, and Japanese don’t have Body Odor?
East Asians particularly Koreans, Chinese, and Japanese sweat but their sweat isn’t smelly like others, this is why they don’t have bad BO. But have you ever wondered about the reason behind it? Well at first glance it might appear to be associated with hygiene and the standard of living of the people there but in reality, it is biological!
So in this post let's explore the reason why East Asians don’t have BO
Sweat
As we all know sweat is just water combined with salts that our body releases onto our skin in order to cool off our body. Contrary to the popular belief, sweat itself is odorless. Then what causes the smell?
In order to understand that kets get familiar with sweat and how it is produced.
Sweat is produced by sweat glands which are present in our skin. They are a type of exocrine gland. Exocrine glands are tissues of glandular origin( glandular means the cells of these tissues produce and secrete something) that produce substances like sweat, tears, saliva, etc., and secrete them onto the epithelium or body surface via tubes. As you can see from the image below, the sweat glands appear like a twisted network of tubes.
We have three types of exocrine glands distributed all over our skin which produce different substances.
- Eccrine sweat glands - produce the sweat
- Apocrine sweat glands - produce a different type of sweat
- Sebaceous glands - produce an oily substance called sebum
Normally the sweat glands present all over our body are eccrine-type glands that produce sweat constituting water and salt. As we get older and hit puberty we start developing the apocrine sweat glands, they are concentrated mostly in the skin of our underarm, pubic region, and scalp. The sweat that they produce is rich in fatty acids, lipids, and hormones. As these apocrine glands will be forming the main platform of our discussion let us understand them better.
The apocrine sweat glands are just a set of hollow tubes lined with glandular epithelium at the base which secrete the sweat via a process called apocytosis. In apocytosis, a part of the cell containing vesicles loaded with molecules like lipids and hormones buds off and breaks, releasing the contents into the ducts of the sweat glands and finally onto the skin surface. This process occurs in all types of apocrine glands, not just apocrine sweat glands. Apart from apocrine, there are two more types called eccrine( also called merocrine) and holocrine. The difference between these is the process through which the molecules are released into the ducts. In eccrine, the process is called exocytosis( the molecules are secreted by the cells into the tubes), while in holocrine the cell ruptures( lysis) and releases the molecules.
Now you may think that these secretions are what makes the sweat smell bad but you would be wrong!
The molecules secreted by the apocrine sweat glands are not the ones responsible for the bad smell, the culprits are the micro-organisms living on our skin!
These microbes are called commensal microbes as they are mostly not harmful and are present in all people. But they do something nasty. They feed on the substances present in our sweat and convert them to odoriferous volatile compounds and these volatile compounds are what cause the bad BO!!
The most common bacterias responsible are Corynebacterium species and Staphylococcus species like S. epidermis and S.hominis. They metabolize the odorless molecules in our sweat to produce malodorous byproducts like thiols and unsaturated fatty acids. Some of the molecules are shown below with the corresponding odor.
In the apocrine cells, there is a protein that is responsible for transporting the molecules present in sweat from the cytoplasm of the cell into small packets called vesicles which later get released onto the skin via the ducts. So some people lack this transporter protein due to which their sweat doesn’t contain the substrates required by the microorganism to produce those foul-smelling compounds. That's why their sweat isn't smelly!
Now, why does this happens?
The answer is Genetics!
Genetics
It is due to a mutation in the ABCC11 gene on chromosome 16. ABCC11 gene encodes for a protein called ABCC11( ATP-Binding Cassette transporter sub-family C member 11). It is a transport protein that moves things across membranes. But if you want to move something then you need energy so this movement occurs at the expense of ATP. It has an ATP binding domain where ATP binds and gets broken down to release energy which can be used to transport molecules against their concentration gradient. This is expressed a lot in apocrine sweat glands. In some people, a point mutation called SNP( Single Nucleotide Polymorphism) occurs which replaces guanine with adenine at a particular location. This results in a wild-type gene which upon translation( producing proteins from the DNA) leads to a change in the peptide chain of the protein.
In the normal protein, the sequence GGG codes for the amino acid Glycine but in the wild-type( where G is replaced by A), the sequence becomes AGG which translates to Arginine. This means in the protein the place where there should have been glycine now there is arginine.
This causes a problem with post-translation N-Glycosylation( a process where sugar groups are added to the polypeptide chain after translation). Arginine interferes with the glycosylation of the protein at an asparagine residue which results in a dysfunctional and wild protein. Now our body has a system in place for getting rid of these dysfunctional proteins, it does so by adding a chain of a molecule called ubiquitin to the wild protein which marks it for destruction. This process of adding ubiquitin is called ubiquitination. Then the marked protein is sent to the proteasome( an organelle that breakdowns and gets rid of misfolded and dysfunctional proteins) where it is destroyed.
All of this means that the body with the mutation lacks the protein required to transport out the molecules which get converted by the skin microbiome into volatile compounds that give sweat its odoriferous smell.
People with these mutations also produce dry cerumen( ear wax). This mutation is found in nearly 95% of South Koreans.