Yellow toenails are usually due to fungal infection in the nails. The fungal infection of the nails is referred to as onychomycosis. The fungal infection of the toenails is more common than that of fingernails. Other than the yellow discoloration, fungal infection of the nails can result in crumbling of the nail edges, pain, thickening of the nails and breaking of the nails.
Although usually not potentially life threatening, yellow toe nails are cosmetically disfiguring and have potential to spread locally. Less commonly, fungal toenail infection can cause permanent nail damage or result in spread of infection. This is more likely in conditions with depressed functioning of the immune system (e.g. anticancer drugs, AIDS, diabetes mellitus, steroid therapy, organ transplant recipients etc.). Hence, immediate treatment is recommended.
The fungi most commonly responsible for the yellow toe nails belong to dermatophyte group. However Candida and some other non-dermatophyte fungi can also cause onychomycosis. Furthermore, there are various subtypes of onychomycosis, and the isolated "yellow toenail" is referred to as distal subungual onychomycosis.
Although fungal infection is the most likely cause of yellow toe nails; rarely, some other disease conditions can also result in yellow toe nails. Some of these conditions are psoriasis, jaundice, paronychia, lymphedema, bronchiectasis, tuberculosis and sinusitis. However, in these conditions, usually there will be other symptoms also and/or involvement of fingernails. Isolated yellow toenail as the only presenting symptom in these conditions is highly unlikely. Trauma to the toes because of tight shoes and frequent use of nail varnish can also result in yellow toe nails.
Treatment of yellow toe nails caused by fungal infection is anti-fungal medication. Anti-fungal medications can be prescribed as systemic (oral) or topical (local application in the form of nail paints, etc.) treatment. The exact choice depends on the particular subtype of onychomycosis and sometimes combined systemic and topical antifungal medications may also be prescribed. Usually prolonged treatment for up to 1 year may be required to fully cure the toenail fungal infection. Recently, few lasers have also been approved for treatment of yellow toe nails.
Treatment of yellow toe nails due to causes other than fungal infection will depend upon the disease causing the yellow toe nails.
Various non-medical home remedies with variety of "natural" products have been proposed but their effectiveness has not been proven yet. Some have modest anti-fungal effect but they are not as effective as the anti-fungal medications.
The fungi causing yellow toe nails require warm, moist and dark environment to grow. Wearing closed shoes for prolonged duration provide this ideal environment for the fungi to grow. Moreover, inadequate personal hygiene also makes one more susceptible to develop toenail fungal infection. Poor blood circulation in the feet and increased sweating also predisposes to toenail fungal infection.
Therefore, preventing measures involve regular washing of the feet with soap and water and allowing them to become completely dry. Wearing shoes for prolonged duration should be avoided as much as possible. Feet should be completely dried before wearing closed footwear. Moisture absorbing socks are better to keep feet relatively dry, especially if one sweats more than usual. Toenails should be adequately trimmed. Regular exercising (walking, running, etc.) helps to improve blood circulation in feet and reduces chances of toenail fungal infection.