In life, we often see some students' faces with brown spots ranging from needles to grain of rice. They are symmetrically distributed, especially on the bridge of the nose and cheeks. This is freckles. The protagonist in the famous Swedish fairy tale "Pippi stockings" is a little girl with freckles on her face. It should be said that freckles are quite common. If you observe freckles under a microscope, you will find that there are many melanin particles in the superficial layer of the skin, indicating that freckles are actually caused by the increase of melanin in the superficial skin.
So why freckles? First of all, genetic genes play a very important role. Medical scientists have found some relevant genetic genes. People with these genes are often more prone to freckles than those without these genes, that is, some people are "born" to freckles.
Secondly, ultraviolet radiation is another "culprit" that promotes the growth of freckles. Many people grow a lot of freckles after sunbathing or going to sunny places for vacation. Medical experts have noticed that freckles grow most on the face, as well as on the head, neck, shoulders and back of hands, but freckles generally do not grow on parts not exposed to the sun. This shows that ultraviolet radiation is a very important inducing factor for the occurrence of freckles.