The treatment of an ingrown toenail partly depends on its severity.

Mild to moderate cases are often treated conservatively with warm water and epsom salt soaks, antibacterial ointment and the use of dental floss. If conservative treatment of a minor ingrown toenail does not succeed, or if the ingrown toenail is severe, surgical treatment may be required. A "gutter splint" may be improvised by slicing a cotton-tipped wooden applicator diagonally to form a bevel and using this to insert a wisp of cotton from the applicator head under the nail to lift it from the underlying skin after a foot soak.

In season 6 of House MD in the episode 12 titled Remorse, House diagnoses his patient with Wilson's Disease in absence of Kayser-Fleischer rings by removing the nail polish to note the blue nails.

Leukonychia (or leuconychia), also known as white nails or milk spots, is a medical term for white discolouration appearing on nails. It is derived from the Greek words "leuko" ("white") and "nychia" ("nails"). The most common cause is injury to the base of the nail (the matrix) where the nail is formed.

It is harmless and most commonly caused by minor injuries, such as nail biting, that occur while the nail is growing. Leukonychia occurs most commonly in healthy individuals, unrelated to any known nutritional or physiological deficiency. When caused by injury the marks will disappear as the nail grows outwards, however a dietary deficiency will cause recurrent leukonychia.

Other possible reasons for this problem with nail colour can be linked to:

- Arsenic poisoning

- Lead poisoning

- Pneumonia

- Heart disease

- Renal failure

- Ill health

- Hypoalbuminemia

- Vitamin deficiency

- Ulcerative colitis

- Hepatic cirrhosis

- Psychogenic stresses

- Onychophagia

- Occupational trauma

- Zinc deficiency

- Protein deficiency

- Psoriasis as well as eczema

- Iron deficiency

Leukonychia striata, transverse leukonychia, or Mees' lines are a whitening or discoloration of the nail in bands or "stria" that run parallel the lunula (nail base). This is commonly caused by physical injury or disruption of the nail matrix. Common examples include excessive tapping of the nails, slamming a car door or extensive use of manicure. It may also occur in great toenails as a result of trauma from footwear. Alternatively, the condition can be caused by heavy metal poisoning most commonly by lead. It can also be caused by cirrhosis or chemotherapy.

The tendency toward leukonychia striata is sometimes inherited in an autosomal dominant fashion. In other cases, it can be attributed to vigorous manicuring and trauma aforementioned, or to a wide variety of systemic illnesses. Serious infections known for high fevers, measles, malaria, herpes, and leprosy may also cause this condition. In many patients, there is no obvious cause, and the streaks resolve spontaneously.

There is a similar condition called Muehrcke's lines (apparent leukonychia) which differs from leukonychia in that the lines fade with digital compression and does not migrate with the growth of the nail.

Available studies lack sufficient power to extrapolate a standardized therapeutic regimen.

As of April 2009, an assessment of the evidence for the efficacy and safety of the treatments for nail psoriasis is in progress.

- Infliximab appears to be the most effective treatment for nail psoriasis to date.

- Results from low-dose acitretin therapy show NAPSI score reductions comparable with those studies evaluating biologic drugs for nail psoriasis and suggest that low-dose systemic acitretin should be considered in the treatment of nail psoriasis.

Trachyonychia, sometimes called sandpapered nails, is a condition characterized by rough accentuated linear ridges (longitudinal striations) on the nails of the fingers and toes. When the condition occurs on all the twenty nails of the fingers and toes, it is known as twenty-nail dystrophy, most evident in childhood, favoring males.

Trachyonychia causes the nails to become opalescent, thin, dull, fragile, and finely longitudinally ridged, and, as a result, distally notched. It can be a manifestation of lichen planus, psoriasis, alopecia areata, immunoglobulin A deficiency, atopic dermatitis, and ichthyosis vulgaris.

"The longitudinal striations can occur as a normal part of the aging process", and not until the nails start to thin and get a sandpaper look is the condition called trachonychia. The nails are opalescent and frequently are brittle and split at the free margin. There has been evidence of the condition as a cutaneous manifestation of lichen planus. It has also been associated with other diseases such as eczema, psoriasis, alopecia areata, and atopic dermatitis. Trachonychia is often seen in vitiligo patients – suggesting that they are more susceptible to this condition.

Beau's lines are deep grooved lines that run from side to side on the fingernail or the toenail. They may look like indentations or ridges in the nail plate. This condition of the nail was named by a French physician, Joseph Honoré Simon Beau (1806–1865), who first described it in 1846.

Beau's lines are horizontal, going across the nail, and should not be confused with vertical ridges going from the bottom (cuticle) of the nail out to the fingertip. These vertical lines are usually a natural consequence of aging and are harmless. Beau's lines should also be distinguished from Muehrcke's lines of the fingernails. While Beau's lines are actual ridges and indentations in the nail plate, Muehrcke lines are areas of hypopigmentation without palpable ridges; they affect the underlying nail bed, and not the nail itself. Beau's lines should also be distinguished from Mees' lines of the fingernails, which are areas of discoloration in the nail plate.

There are several causes of Beau's lines. It is believed that there is a temporary cessation of cell division in the nail matrix. This may be caused by an infection or problem in the nail fold, where the nail begins to form, or it may be caused by an injury to that area. Some other reasons for these lines include trauma, coronary occlusion, hypocalcaemia, and skin disease. They may be a sign of systemic disease, or may also be caused by an illness of the body, as well as drugs used in chemotherapy or malnutrition. Beau's lines can also be seen one to two months after the onset of fever in children with Kawasaki disease.

Human nails grow at a rate which varies with many factors: age, and the finger or toe in question as well as nutrition. However, typically in healthy populations fingernails grow at about 0.1mm/day and toenails at about 0.05mm/day. With this in mind the date of the stress causing Beau's lines and other identifiable marks on nails can be estimated. As the nail grows out, the ridge visibly moves upwards toward the nail edge. When the ridge reaches the nail edge, the fingertips can become quite sore due to the mis-shapen nail pressing into the flesh deeper than usual, exposing the sensitive nail bed (the quick) at the nail edge.

A researcher found Beau's lines in the fingernails of two of six divers following a deep saturation dive to a pressure equal to 305 meters of sea water, and in six of six divers following a similar dive to 335 meters. They have also been seen in Ötzi the Iceman.

Mees' lines or Aldrich–Mees' lines, also called leukonychia striata, are white lines of discoloration across the nails of the fingers and toes (leukonychia).

Koilonychia (from the Greek: koilos-, "hollow", onikh-, "nail"), also known as spoon nails, is a nail disease that can be a sign of hypochromic anemia, especially iron-deficiency anemia. " It refers to abnormally thin nails (usually of the hand) which have lost their convexity, becoming flat or even concave in shape. In a sense, koilonychia is the opposite of nail clubbing. In early stages nails may be brittle and chip or break

easily.

Koilonychia is associated with Plummer-Vinson syndrome and iron deficiency anemia.

Dyschromia refers to an alteration of the color of the skin or nails.

"Hyperchromia" can refer to hyperpigmentation, and "hypochromia" can refer to hypopigmentation.

"Dyschromatoses" involve both hyperpigmented and hypopigmented macules.

Research suggests that fungi are sensitive to heat, typically . The basis of laser treatment is to try to heat the nail bed to these temperatures in order to disrupt fungal growth. As of 2013 research into laser treatment seems promising. There is also ongoing development in photodynamic therapy, which uses laser or LED light to activate photosensitisers that eradicate fungi.

There exist numerous treatments for nail psoriasis but there is little information concerning their effectiveness and safety.

Treatments include topical, intralesional, radiation, systemic, and combination therapies.

- Tacalcitol ointment obtains a significant improvement in all nail parameters, both of the matrix and of the bed.

- Clobetasol nail lacquer and tacalcitol ointment

- 5-fluorouracil. A reported side-effect is yellow nails

- Calcipotriol

- Calcipotriol plus betamethasone dipropionate ointment.

- Efalizumab

- Infliximab

- Golimumab

- Low dose methotrexate

- Intralesional corticosteroid injection

Onychorrhexis (from the Greek words ὄνυχο- "ónycho-", "nail" and ῥῆξις "rhexis", "bursting"), also known as brittle nails, is a brittleness with breakage of finger or toenails that may result from excessive strong soap and water exposure, nail polish remover, hypothyroidism, anemia, anorexia nervosa or bulimia, or after oral retinoid therapy. Onychorrhexis affects up to 20% of the population.

There does not yet exist a specific treatment for IP. Treatment can only address the individual symptoms.

Terry's nails is a physical condition in which a person's fingernails or toenails appear white with a characteristic "ground glass" appearance without any lunula. The condition is thought to be due to a decrease in vascularity and an increase in connective tissue within the nail bed. It frequently occurs in the setting of liver failure, cirrhosis, diabetes mellitus, congestive heart failure, hyperthyroidism, or malnutrition. Eighty percent of patients with severe liver disease have Terry's nails, but they are also found in patients with kidney failure, in patients with congestive heart failure and are described as a brown arc near the ends of the nails. The recognition of characteristic nail patterns, such as Terry’s nails, may be a helpful herald for early diagnosis of systemic diseases.

This was named for Dr. Richard Terry.

ICD 10: L60.8

Blue nails, or more formally azure lunula, are characterized by a blue discoloration of the lunulae, seen in argyria and cases of hepatolenticular degeneration (Wilson's disease), also having been reported in hemoglobin M disease and hereditary acrolabial telangiectases.

In Wilson's disease the blue color involves the lunula (most intense pigmentation) and fades proximally. In argyria, the nail is permanently pigmented a slate-blue color and is most evident in the lunula. Minocycline and Zidovudine can also turn the nail plate blue-gray. There are also reports of hydroxyurea as a rare cause.

Hapalonychia, also known as egg-shell nail, is a condition in which the top of a toe or finger nail becomes soft and thin, causing it to bend or break. This condition can manifest as a result of genetic discrepancy and may also occur due to malnutrition and debility. Nails are often a representation of the internal nutritional of health. Although overall well-being is not typically determined by nail health, fissures, breaks and calcium spots are minor indications of inner health. Hapalonychia may also be attributed to myxedema, rheumatoid arthritis, anorexia, bulimia, Hansen's disease, Raynaud phenomenon, oral retinoid therapy, or radiodermatitis.

Carotenemia and carotenoderma is in itself harmless, and does not require treatment. In primary carotenoderma, when the use of high quantities of carotene is discontinued the skin color will return to normal. It may take up to several months, however, for this to happen. Infants with this condition should not be taken off prescribed vitamin supplements unless advised to do so by the child's pediatrician.

As to underlying disorders in secondary carotinemia and carotenoderma, treatment depends wholly on the cause.

Chemical (keratolytic) or surgical debridement of the affected nail appears to improve outcomes.

As of 2014 evidence for laser treatment is unclear as the evidence is of low quality and varies by type of laser.

As of 2013 tea tree oil has failed to demonstrate benefit in the treatment of onychomycosis. A 2012 review by the National Institutes of Health found some small and tentative studies on its use.

Treatment of manifestations: special hair care products to help manage dry and sparse hair; wigs; artificial nails; emollients to relieve palmoplantar hyperkeratosis.

Mees' lines appear after an episode of poisoning with arsenic, thallium or other heavy metals, and can also appear if the subject is suffering from renal failure. They have been observed in chemotherapy patients.

Severe congenital onychogryphosis affecting all twenty nailbeds has been recorded in two families who exhibit the dominant allele for a certain gene. Congenital onychogryphosis of the fifth toe (the little toe) is fairly common, but asymptomatic and seldom brought to the attention of medical professionals. Rather, it is brought to the attention of manicurists who routinely file the clawed toenail flat.

In 2016, interferon gamma/CXCL10 axis was hypothesized to be a target for treatments that reverse inflammation. Apremilast is undergoing investigation as a potential treatment .

Dermatopathia pigmentosa reticularis (DPR), also known as dermatopathia pigmentosa reticularis hyperkeratotica et mutilans, dermatopathia pigmentosa reticularis hypohidotica et atrophica and dermatopathic pigmentosa reticularis, is a rare, autosomal dominant congenital disorder that is a form of ectodermal dysplasia. Dermatopathia pigmentosa reticularis is composed of the triad of generalized reticulate hyperpigmentation, noncicatricial alopecia, and onychodystrophy.