My daughter had an ingrown toenail. It has happened before and I wondered why.
Toenails are made from a tough, fibrous protein called keratin. The nail plate is formed in the matrix (not the one with Keanu, but the region under your skin at the base of the nail). The lighter coloured crescent at the base of nails is called a lunula and is part of the matrix too.
icking things off, epithelial cells in the matrix grow, divide and die. They contain keratin, which remains after the cells die and lose their nucleus and other organelles. An enzyme called transglutaminase (sometimes used as meat glue) packages the keratin with other proteins and lipids. Pressure from the matrix pushes the keratinized cells out toward the tips of your toes. The leading edge of the nail depends on the shape of the edge of the matrix. The hardness depends on the thickness of the keratin and the amount of cross-linking within it. The nail grooves—the folds in the skin along the sides of the nail, guide the nail forward.
Toenails grow about 1.6 mm per month. Metabolism and blood flow affect the rate of growth, and nails in general tend to grow more quickly when you are younger, if you are male, and in the summer. Growth rate may also be related to how much the fingers are used. Terminal trauma, the little injuries incurred by use, stimulate blood flow and nail growth. This may explain why fingernails grow more quickly than toenails and why fingernails grow more quickly on your dominant hand but not between feet (if you are mostly sitting around with socks and shoes on). Tiny structures attach the nail to the nail bed—the skin under the nail. These structures can bind and unbind to allow the nail to slide forward. So the nail has the stress of being pushed forward by growth and pulled down by adhesion, which results in a residual stress over the entire nail.
Onychocryptosis, or ingrown toenail, occurs when the corners of the nail irritate the nail grooves. Ingrown toenails are much more common in the big toe. This has been my experience too. According to a mathematical model of nail growth, residual stress tends to be greater in larger nails. Ingrown toenails are more common in children whose nails are growing quickly and in pregnant women, because of the increased stress on their feet.
Trimming toenails too short is a common cause for ingrown toenails because then the nail groove is more likely to overlap with the corner of the nail. Wearing tight shoes or getting toe injuries can make it worse. If you are born with more curvy nails, you will be more prone to these problems. When the nail digs into the skin, it can become infected, pus can come out and it might smell worse than usual. If you let things go, then the doctor might have to hack off the part of the offending nail with one of various methods. It seems best to keep on your toes and keep your toenails in good shape before it comes to that.
If you care to share toe care tips, please do.