Why do my toenails darken?

A change in the color of the nails can be caused by various disease entities, m.in.: - Chronic disease, such as anemia, diabetes, heart disease, chronic kidney disease. - Melanoma, which is a very dangerous skin cancer, can manifest itself in black or brown spots, also under the nail. - Nail injuries can also cause a change in the color of the toenails and this is the result of damage to the vessels that bring and drain blood to the nail, causing bleeding under the nail, resulting in its black coloration. - Fungal infection - usually, however, the toenails are white or yellow in color, however, sometimes they can cause their black coloration. However, if you do not know why the nails have changed color, it is worth going to the doctor, in case it is a symptom of a more serious disease. I also encourage you to read the article: https://www.gdziepolek.pl/artykuly/grzybica-paznokci-jak-zapobiegac-i-leczyc