Athletes will often encounter a problem with their toenails turning dark. For a black toenail, that is. Fungal nail infections may be classified according to the part of the nail affected. This can also occur in people who have worn a tight shoe for a prolonged period of time. I can see where he is coming from, sometimes depression is a normal and natural response to a situation. The lines indicate low levels of protein in the blood. The damaged cause to the toenail may allow the establishment of a fungal infection in the nail.
Blue nails are also caused by problems that reduce the amount of oxygen in the blood, such as asthma and COPD, severe anemia, cold exposure, exposure to high altitude, peripheral arterial disease, or shock. Noticeable changes, such as temperature, skin color, pain, or swelling may be warning signs for poor circulation or loss of sensation that could potentially lead to something more serious. If you drop something heavy on your foot or stub your