One of the earliest symptoms of fingernail fungus is a yellowish or brownish discoloration of the fingernail. It's mild, and may go unnoticed, especially if you wear nail polish, but it will likely progress over time. The color change is the result of the fungus producing colored pigments as it grows and gets established under the fingernail.

Fungus grows slowly in fingernails and toenails, so the yellow color may be the only sign of infection you see for quite a while. It's likely that in some instances, the body's immune system succeeds in fighting off the fungal infection: if this happens, the discoloration will go away. The immune system finds it hard to fight the fungus, however, because the growth is actually extending into the nail itself, where antibodies and immune cells can't go. In many cases, therefore, the fungus grows unchecked, and before too long, more symptoms of fingernail fungus appear.

More advanced symptoms of fingernail fungus occur when the nail starts to come apart. Fingernails and toenails are actually made up of dead cells, similar to skin cells: at the root of the nail, the dead cells are piled in layers, like many layers of autumn leaves, packed tightly together. As more and more nail forms at the root, it pushes the rest of the nail out onto the nail bed. When fungus begins to grow through these layers of cells, they come away from each other - that is why one of the symptoms of fingernail fungus is a thickened flaky nail. The discoloration may get worse as well because there is more growth of fungus there, and more pigment being produced.

Fingernails and toenails, and hair, contain a protein called keratin. The outer layer of dead skin cells all over our bodies also contains this protein: it serves as a horny protective covering for our skin. This protein is the main nutrient source for the types of fungi that grow on human skin and hair, and this explains why fungal nail infections frequently spread to the surrounding skin. Thus, one of the symptoms of fingernail fungus, especially if it has been untreated for a while, is flaking, scaling skin, and even redness and inflammation of the fingers and toes around infected nails.