Human skin has always been the subject of study by scientists, and it is not surprising that they keep finding new and interesting features in it. Among them are secret stripes and other mysterious markings that are not visible to the naked eye, but are the result of the formation of our covering layer. Although we cannot see these patterns on our skin, they can appear in a variety of skin conditions, including eczema and vitiligo.
History of Secret Stripe Discovery
By the early 20th century, German dermatologist Alfred Blaschko studied the skin of more than 150 patients and noticed patterns of moles, birthmarks and other skin conditions on their bodies. He found that they followed established lines that were present at birth and did not follow any other known body system, such as blood vessels or nerves. Instead, they create broad arches of breasts, mountainous shapes on their backs, and twisted loops on their buttocks.
Additional details, including scalp spirals and neck curves, were added to the map 100 years later by physician Rudolph Happle. It is now believed that these Blaschko lines trace the pathways of our cells, which divided and grew into the skin we are now in, during embryonic development.
How the secret bands come into being
Specifically, secret bands are directed by keratinocytes – the main cells in our surface skin – and melanocytes – the cells deep in the epidermis responsible for our skin pigment. Melanocytes form in the neural crest of the embryo when we are still just a blob of a few hundred cells. Around this stage of development in females, the cells begin to randomly choose which X chromosome to turn off, since we only need one active one per cell, but we inherit two, one from mom and one from dad.
So, some of the embryonic cells that give rise to our skin cells will have dad’s X chromosome and others will have mom’s. All of the cells that divide with these early cells will retain the same epigenetic X chromosome tuning, which means that the entire Blaschko line will also have this version of DNA, while the line next to it may be the same or may have a different X chromosome.
Mosaicism and pigmentary mosaicism
This is why some patterns are represented as lines and others as larger patches. This patchwork quilt of genetic patterns is called mosaicism and can occur with mutations that occur early in development, not just traits associated with the X chromosome.
Mutations affecting color-producing cells can lead to pigmented mosaicism, manifesting as stripes and curls following the Blaschko lines. Types 1a and 1b in the image are the most common varieties, while others are less common.
Patterns on the skin of animals
While secret stripes and other markings on the skin are not always visible in humans, in some animals they are a major feature of coat coloration. The coat color genes are exclusively linked to the X chromosome in some animals, such as cats. This is how we get chintzy cats, in which the color spots clearly indicate where each of the two different cell types is located, one group with the mother’s X chromosome and the other with the father’s.
In conclusion, we can say that the secret stripes and other mysterious markings on human skin are the result of the formation of our covering layer, which occurs during embryonic development. Although we cannot see these patterns on our skin, they can appear in a variety of skin conditions, including eczema and vitiligo. And in animals, they can be a major sign of wool coloration.
