In this blog post, we’ll examine what “dirt”—which we often consider unsanitary—is actually made of, and how excessive scrubbing affects skin health.
These days, public bathhouses are becoming increasingly rare—it’s hard to spot one while walking down the street. Even when you do visit a bathhouse, the number of professional scrubbers who charge a fee to remove dead skin has dwindled, so most people end up scrubbing themselves at home. While doing this at home, everyone has probably wondered at least once, “Wouldn’t it be enough to just take a quick shower without scrubbing?” However, most people likely believe that dead skin must be removed without fail, based on childhood experiences where their parents would scrub them until no more dead skin came off. These days, though, doctors appearing on television sometimes say that avoiding excessive scrubbing is actually better for skin health. Perhaps as a result, more people are opting to simply take a quick shower using a washcloth or body wash instead of scrubbing. So, which is the better choice for physical health: scrubbing off dead skin or leaving it alone?
What we commonly refer to as “dead skin” is a substance formed by a mixture of dead skin cells, sebum, sweat, and external dust that has accumulated on the skin’s surface. Not all components of dead skin can be considered fine dust, though fine dust may constitute a portion of it. Fine dust generally refers to particulate matter with a diameter of 10 μm (micrometers, one-millionth of a meter) or less. When it accumulates over a long period on the surfaces of inanimate objects, such as desks or books, it becomes ordinary dust; however, when it adheres to human skin, it mixes with dead skin cells, sebum, and sweat shed by the skin, becoming part of the substance we commonly call “dirt.” Dead skin cells are the material produced when keratinocytes—the cells in the outermost layer of the skin—naturally shed at the end of their life cycle. A classic example is when the skin becomes dry in winter and flakes off as white scales. In this way, grime is formed when dead skin cells shed from the skin mix with sebum, sweat, and external dust.
Unlike the grime formed when external dust mixes with sebum, sweat, and dead skin cells produced by the body, what about the grime that accumulates under fingernails? Even among people with long nails, some accumulate a lot of grime under their nails while others hardly do; this primarily depends on hand-washing habits and the extent to which foreign particles get trapped under the nails. It cannot be concluded that the grime under fingernails consists mostly of fine dust; it may be a mixture of dead skin cells shed from the skin, sebum, dust, and various foreign substances picked up from daily environments. Therefore, if you notice a lot of foreign matter trapped under your fingernails, it is advisable to develop the habit of washing your hands thoroughly on a regular basis. Concepts somewhat similar to this foreign matter under fingernails are scalp oil and dandruff. Oily hair results from sebum secreted by the sebaceous glands on the scalp that coats the hair, while dandruff consists of dead skin cells that have shed from the scalp. However, dandruff is not caused solely by a lack of sebum leading to a dry scalp. Various factors may be involved, such as sebum on the scalp, microorganisms like yeast present on the skin, skin condition, and hair care habits. Therefore, the presence of both oily hair and dandruff does not necessarily mean that a person simply does not wash their hair properly.
“Grime” does not appear only on the human body. The substance we call “soap scum,” commonly found in bathrooms and sinks, refers to a buildup formed either by precipitates resulting from metal ions—such as calcium or magnesium—in the water combining with soap components, or by the accumulation of dead skin cells shed during washing and showering mixed with soap residue. In other words, the grime we find on our bodies and the soap scum found in bathrooms differ in both their formation process and composition. While body grime is formed by a mixture of dead skin cells, sebum, sweat, and external dust, soap scum in the bathroom is often created when metal ions in the water combine with soap components. Thus, even though we commonly refer to both as “grime,” they have different characteristics depending on where they form and their composition.
So, does this grime actually play a beneficial role for our skin? To answer the question first, while grime itself cannot be considered a beneficial substance for the skin, the stratum corneum on the skin’s surface and the microorganisms coexisting with the skin play an important role in protecting it. The skin is not merely a barrier against external substances but a complex environment where various microorganisms coexist; some of these microorganisms help inhibit the growth of other microorganisms or regulate the skin’s immune response. In fact, research continues to show that microorganisms normally present on the skin, such as Staphylococcus epidermidis, can inhibit the growth of pathogenic microorganisms and influence the skin’s immune response. Therefore, unconditionally removing all microorganisms from the skin’s surface is not necessarily beneficial for skin health. However, not all microorganisms on the skin are beneficial; if the skin barrier is damaged or certain conditions arise, even microorganisms that normally pose no problem can cause infections. The key is not to eliminate all microorganisms from the skin, but to manage the skin barrier and the microbial ecosystem so that they maintain an appropriate balance.
That said, this does not mean you should neglect to wash away dead skin cells, sebum, sweat, and other substances that accumulate on the skin. Sebum and sweat secreted by our bodies, as well as dead skin cells shed from the skin, contain various organic substances. When these substances accumulate excessively on the skin’s surface or mix with other substances, they can produce unpleasant odors. In particular, in warm, humid, and poorly ventilated environments, microorganisms easily produce odor-causing substances. Areas where the skin folds or tends to become damp, such as the armpits and groin, are prime examples. Therefore, it cannot be said that completely avoiding the removal of grime is the correct approach for skin health. While keeping the skin clean is necessary, this does not necessarily mean vigorously scrubbing the skin to remove dead skin cells.
We often think of the presence of grime as a sign of dirtiness. However, it is a natural phenomenon for a mixture of dead skin cells, sebum, sweat, and external dust to accumulate on the skin’s surface. Furthermore, the skin’s stratum corneum is a crucial component of the skin barrier that protects the skin from external irritants and reduces moisture loss; therefore, removing it more vigorously than necessary can irritate the skin, leading to dryness or damage to the skin barrier. Therefore, rather than trying to completely strip the skin’s surface by scrubbing too hard just because you see grime, it’s important to cleanse appropriately using methods that don’t irritate the skin. This is especially true for those with sensitive or dry skin, who should avoid excessive friction and choose a cleansing routine suited to their skin’s condition. It is best to move away from the mindset that dead skin cells must be removed simply because they are visible, and instead cleanse the skin just enough to maintain its health. Of course, there is no need to refuse to wash altogether just because dead skin cells are present on the skin. This is because the habit of not washing can have a negative impact not only on skin condition but also on body odor, hygiene, and interpersonal relationships.
