A variety of disorders can affect nails, including deformities, infections of the nail, paronychia, and ingrown toenails. Nail changes may occur in many systemic conditions and genetic syndromes or result from trauma.
Most nail infections are fungal (onychomycosis), but bacterial and viral infections can occur (eg, green-nail syndrome [Pseudomonas], herpetic whitlow [herpes simplex virus-1]). Even parasitic infestation such as crusted scabies can lead to changes in the nail plate. Paronychia is not actually an infection of the nail but rather of periungual tissues.
Common warts (verrucae vulgaris) result from human papillomavirus infection and frequently infect the proximal nail fold and sometimes the subungual area. Onychophagia (nail-biting) can help spread this infection. Warts involving these areas are especially difficult to treat.
Toenails require special attention in the elderly and in people with diabetes or peripheral vascular disease; a podiatrist can help avoid local breakdown and secondary infections by assisting in routine nail trimming.