Black fungus under fingernails is about the last thing that anyone would want, yet fungal nail infection is not at all uncommon. Fungal fingernail infection happens when fungal spores get in under the fingernails and start to grow there. Before long fungal hyphae (slender branching stalks of fungal growth) are wending their way back from the tip of the nail toward the cuticle, flourishing in the warm moist environment of the nail bed and deriving nourishment from the finger nail itself. Not all fungi produce a black color however: a yellow or brown color is even more typical.

A subtle yellowish tinge to the nail is often the first sign of fungal nail infection and it usually starts on one or more toenails. Stronger colors, such as dark brown or black, develop over time as the fungus matures and begins producing spores. Furthermore, there is great variation in what nail fungus looks like, and some infections simply have a white or cream color. Black fungus under fingernails is not really a typical fingernail infection.

What nail fungus looks like depends on a variety of factors: what type of fungus is growing in the nail, how far advanced the infection is, which parts of the nail are affected, and whether there have been any attempts at treatment. Black fungus under fingernails would usually be a fairly advanced infection. Other symptoms in advanced infection include nails that are thick and deformed, crumbling or flaking nails that wear away quickly, painful toes and fingertips, peeling skin around the affected nails.

If you have black fungus under fingernails, and your toenails are not infected, you may have caught it when your hands came in contact with fungal elements in the soil, or in decaying vegetation. It is always a good idea to wear gardening gloves when you are working in the garden, and to clean your nails thoroughly if dirt lodges under them. Be wary, too, of any little cuts and scratches you get on your hands while you are working outside: these make it easier for any harmful organism, including fungi to invade your nails and skin. Places to pick up a nail fungus include contact with someone else's nail infection, and damp public places such as pools and public showers stalls. Manicures and pedicures in nail spas have also been known to spread fungus infections. Take care of your nails and keep in mind what nail fungus looks like, so you can recognize it quickly and get treatment before it gets too bad.