Accidental injury to fingernails and toenails are common, often from being crushed, such as when caught in a closing door, from some type of pressure, such as when wearing poorly fitting shoes, or from a cut. Though these injuries are not usually serious, they can be painful.
Whether covering the tip of a finger or toe, a nail is a protective curved plate made of keratin, the same protein that is found in hair. The nail grows from the nail bed at the base of the nail, where the half-moon shape lunula that is partially covered by the cuticle (the flap of skin at the base of the nail) is found.
Types of nail injury
Most people will be familiar with having a small white spot on a fingernail at some point in their lives. It is a minor injury to the nail that eventually disappears as the nail grows and is trimmed without much thought or inconvenience. However, a more serious injury, such as damage to a nail bed, can lead to permanent nail deformity.
An injury to a nail may result in the loss of the nail. As long as the nail bed itself wasn't damaged, a lost nail should eventually grow back. Healthy fingernails grow at a rate of about 0.10mm per day, but toenails are slower, growing at only about one half to one third of a fingernail's rate. Nail growth is slower when ageing or diseases that reduce blood flow to the hands and feet are involved.
Physical changes in the nails that can indicate an injury, with or without pain, include:
- Brittle, splitting or peeling fingernails: these often occur in people who frequently expose their hands to water, strong soaps or chemicals.
- Little white spots: known as leukonychia, these often appear after a minor injury and will go away on their own, though it can take weeks or months.
- Grooves or deep lines across the nail: known as Beau's lines, they are often noticed a few months after an injury, once the nails grow and the grooves move up along the nail.
- A thin red to brown streak of blood under the nail, running in the direction of the nail's growth: this is a splinter haemorrhage, which can be caused by damage to tiny blood vessels under the nail, but if more than one nail is affected it may be caused by bacterial endocarditis.
- Nail turns black or purple-black after an injury: referred to as a subungual haematoma, it is caused by blood collecting under the nail; it will disappear as the injury heals.
- Thickening of the nail plate: known as onychogryphosis, this often occurs on big toes in elderly people due to an injury or poorly fitted shoes, as well as poor blood circulation.
- Nail detaches partially or fully from the nail bed: known as onycholysis, it can be caused by a trauma or chemicals as well as certain skin conditions; it will not reattach and you'll need to wait for about six months for a fingernail to grow back fully or 18 months for a toenail.
- A cut (laceration) goes through the nail, nail bed and/or cuticle: it can be minor or severe, including the nail being lifted off the nail bed or part of the finger tip being amputated.
In addition to being injured, the shape and texture of the nails may change due to ageing or disease, and nails can be affected by a fungal nail infection. If you are not sure if a black, brown or purple colouration was caused by an injury, or it doesn't seem to be going away, seek medical advice to rule out the possibility of an underlying condition such as melanoma.