In fact, at night, umbilical demons put the pellets and villi from clothes in the deep umbilical scars, which they tear off the clothes.
Technically, there are two kinds of navels. Some people may have a flat or even bulging navel, but in most people, the navel forms a pronounced depression about a centimeter in diameter. Naturally, small objects can fall into such a depression, or, for example, water can accumulate.
According to one of the theories, the main mechanism for the formation of pellets in the navel is traditionally the accumulation of clothing villi and accompanying debris in the umbilical scar. Naturally, the villi fall from clothes constantly during wearing and this happens throughout the body, however, for most people, the navel is the only place favorable for their accumulation on the body. In addition to the dependence of the color and nature of the pellets on the color of the clothing, there is also a dependence of the number of pellets on the presence of hairs directly in the navel and within it.
In general, from the point of view of the physics of the process, several main factors can be identified that affect the process accumulation of pellets:
the shape of the navel (it is logical that convex navels cannot accumulate pellets);
"accessibility" of the navel (for example, in obese people, the navel may be covered by a fold of skin, which, on the one hand, prevents small particles from entering the navel, and on the other hand, prevents them from leaving it);
the presence of hair in the navel area (hair traps the villi and helps them to become matted);
features of the fabric of clothing that is adjacent to the torso (for example, new cheap T-shirts are more prone to the formation of fine lint than, say, an expensive and already worn silk shirt);
human hygiene regimen (if you pay due attention to the hygiene of the navel, then the pellets will simply not have time to accumulate);
other factors (for example, a person may deliberately provoke pellets - see the Guinness Book of Records).
So, answering the question, we can say that most of the owners of belly buttons are in some way a risk zone in terms of the formation of pellets in the navel, but due to habits, lifestyle and upbringing they may never collide. However, the formation of pellets in the navel itself is a fairly common phenomenon.
It should be said that the presence of pellets in the navel as such does not pose a great danger. However, it is believed that under certain conditions, pellets and debris in the navel, together with sweat and body secretions, can become a favorable environment for development, which in turn can lead to inflammatory processes of the umbilical scar and concomitant diseases. Also, similar processes can occur in other areas favorable for this - skin folds, scars, auricles ... And this becomes especially important in the summer.