Fingernail or toenail abnormalities can tell you a lot about your health. They're often a sign of a fungal nail infection or injury, but can sometimes indicate a more serious underlying condition.
See your GP if your nails have changed in colour, texture, shape or thickness and you don't know why (for example, you haven't injured your nails or been biting them).
Below are the most likely reasons for the following nail problems:
Brittle or crumbly nails
Brittle nails are often just a sign of ageing or long-term exposure to water or chemicals such as detergents and nail polish.
Wearing gloves will help protect your nails while doing work where your hands are exposed to water. Regularly applying moisturising cream to your fingers and nails will also help protect them.
Sometimes, brittle or crumbly nails can be caused by:
Reactive arthritis is a less common cause of crumbly nails. It's an unusual reaction of the immune system affecting the joints, muscles and other parts of the body following an infection. If you have a combination of symptoms affecting different parts of your body, your GP might consider this condition.
The most common causes of a yellow nail are fungal nail infections or nail psoriasis.
Yellow nails can also be caused by any of the following:
- frequent application of nail varnish
- lymphoedema – a long-term condition that causes swelling of the skin
- permanent damage to your airways caused by bronchiectasis – a long-term lung condition
- sinusitis – inflammation of the lining of the sinuses
- inflammation of the thyroid gland, found in the neck
- tuberculosis (TB) – a bacterial infection affecting the lungs
- jaundice (yellowing of the skin) – caused by liver disease
- some medications, such as mepacrine or carotene
- chronic paronychia – infection of the nail fold
Green-black nails can be caused by overgrowth of bacteria called pseudomonas, particularly under loose nails. It can be treated by applying antibiotic eye drops underneath the nails or soaking the affected nails in an antiseptic solution or vinegar.
Grey nails can be caused by medications such as antimalarials or minocycline.
Brown nails can sometimes be caused by thyroid disease, pregnancy, malnutrition and frequent use of nail varnish.
Red or yellow drop under the nail
If the discolouration looks like a drop of oil under the nail or is the colour of salmon, you may have psoriasis of the nails.
Half white, half brown nails
Fingernails that are half white and half brown (brown near the tips) can be a sign of kidney failure, where the kidneys stop working properly.
The link isn't fully understood, but one theory is that kidney failure causes chemical changes in the blood that encourage melanin (a skin pigment) to be released into the nail bed. It's also possible that kidney failure causes an increase in the number of tiny blood vessels in the nail bed.
It's estimated up to 40% of people with kidney failure have "half-and-half" fingernails. They also sometimes occur in people with AIDS and those who've had chemotherapy.
If most of the nail has turned white and it isn't because it has become detached from the nail bed, it's likely to be either a fungal nail infection or a sign of decreased blood supply to the nail bed, which causes something known as "Terry's nails".
Terry's nails are typically white with reddened or dark tips and can be a sign of a wide range of medical conditions, including:
Thickened, overgrown nails
A common cause of thickened nails is a fungal nail infection. This can also cause them to discolour and become crumbly (see above).
Other possible causes of thickened or overgrown nails are:
- psoriasis – a long-term condition that tends to also cause red, flaky patches of skin
- long-term pressure from shoes that are either too small or too narrow over the toes
- reactive arthritis – where the immune system attacks the joints, muscles and other parts of the body following an infection
Severely overgrown horn-like nails
Sometimes, the toenails become so overgrown and thickened that they resemble claws and are almost impossible to cut with conventional nail clippers. This nail disorder, known as onychogryphosis ("ram's horn nails"), is seen in older people or as a response to long-term pressure on the nails. Regular chiropody can help, but sometimes the nails need to be removed by a podiatrist or doctor.
It's normal for a toenail to come loose and fall off after an injury to the toe. Another common cause of a loose nail is over-manicuring the nails and cleaning underneath them with a sharp object.
Less commonly, a loose nail may be a sign of one of the following health conditions:
- a fungal nail infection
- psoriasis of the nail
- warts that cluster around the fingernail
- an overactive thyroid
- sarcoidosis – a condition where small clumps of cells form in the organs and tissues of the body
- amyloidosis – where protein builds up in the organs
- a problem with the connective tissue fibres in the body that support the organs and body tissues
- poor circulation – for example, caused by smoking or Raynaud's phenomenon (a condition where the blood supply to the fingers and toes is affected, causing them to turn white)
- an allergic reaction to medicine (usually to a type of antibiotic) or nail cosmetics
A loose nail should be cut back to where it's detached to allow the nail to become reattached as it grows. You shouldn't clean your nails with anything other than a soft nailbrush.
Indented spoon-shaped nails (koilonychia)
If your fingernails curve inwards like spoons (koilonychia), you may have one of the following disorders:
Pitting or dents on the nails
Pitting or small dents on the surface of your nails can be a sign of any of the following conditions:
- eczema – a long-term skin condition that causes the skin to become itchy, red, dry and cracked
- reactive arthritis
- alopecia areata – a condition that causes temporary bald patches on the scalp that are about the size of a large coin
Grooves across the fingernails (Beau's lines)
Deep lines or grooves that go from left to right across the nail are known as Beau's lines. They may occur as a result of:
- a previous illness – the line forms at the time of the illness
- having chemotherapy
- a previous injury
- previous exposure to very cold temperatures, if you have Raynaud's phenomenon
Illness, injury or cold temperatures can interrupt nail growth and cause nail grooves to form at the base of the nails.
The grooves tend to only be noticed a few months later, when the nails have grown and the grooves have moved up the nails to become visible. It takes about four to six months for a fingernail to fully grow out, and six to 12 months for a toenail.
Unusually curved fingertips and nails
Clubbing of the fingertips means the tissue beneath the nails thickens and the fingertips become rounded and bulbous. The fingernails curve over the rounded fingertips.
Clubbing is thought to be caused by increased blood flow to the fingertips. It can run in families and be completely harmless. However, if it suddenly develops, it may be a sign of one of many possible medical conditions, including:
White lines running across nails
White spots or streaks are normal and nothing to worry about, but parallel white lines that extend all the way across the nails, known as Muehrcke's lines, are a sign of low levels of protein in the blood. In contrast to Beau's lines, they're not grooved. They can occur as a result of liver disease or malnutrition.
Dark stripes running down the nail
Dark stripes running down the nails (linear melanonychia) are fairly common in black people over 20 years of age, and in most cases it's perfectly normal.
However, dark stripes shouldn't be ignored because it can sometimes be a form of skin cancer that affects the nail bed, called subungual melanoma. It's important that your doctor checks it to rule out melanoma.
Subungual melanoma usually only affects one nail. It will also cause the stripe to change in appearance – for example, it may become wider or darker over time and the pigmentation may also affect the surrounding skin (the nail fold).
Red or brown little streaks under the nails
If you have little red or brown streaks underneath your nails, it's likely they're splinter haemorrhages – lines of blood caused by tiny damaged blood vessels.
A few splinters under one nail are nothing to worry about, and are most likely caused by an injury of the nail. However, if many nails are affected, the splinters may be a sign of lupus erythematosus, psoriasis, an infection of the heart valves (endocarditis) or another underlying condition.
A destroyed nail
Nails can be destroyed by:
- injury, including nail biting
- skin conditions, such as psoriasis or lichen planus
- overgrowth of the surrounding tissues, which is usually harmless – for example, caused by a wart or verruca
- overgrowth of the surrounding tissues caused by skin cancer (this is rare)
- nail patella syndrome – a rare genetic condition which may cause missing nails, usually at birth
See your GP if one of your nails is destroyed and you don't remember injuring it.
Painful, red and swollen nail fold (paronychia)
Paronychia is inflammation of the nail fold (the skin and soft tissue that frames and supports the nail).
It's most commonly caused by infection, injury or irritation, and is about three times more common in women than in men. Sometimes, it's associated with an underlying skin condition, such as eczema or psoriasis, or another medical condition, such as diabetes or HIV.
Paronychia can develop over a few hours (acute paronychia). If it lasts for more than six weeks, it's known as chronic paronychia.
Acute infective paronychia usually starts after a minor injury to the nail fold, such as from nail biting, picking or manicures. The affected area is red, warm, tender and swollen. After a while, pus can form around the nail and may lift the nail.
Acute paronychia is often the result of a Staphylococcus infection, but it can sometimes be caused by the virus responsible for cold sores (herpes simplex virus). In this case it's known as herpetic whitlow.
Treatment for acute paronychia includes antibiotic creams or tablets. If there's a large amount of pus, surgically draining it can help. With treatment, an infected nail fold can clear up in a few days. If it isn't treated or doesn't respond to treatment, the problem can become long-term (chronic).
Chronic paronychia often affects people who have their hands in water for long periods, or come into contact with chemicals, such as cleaners, bartenders, canteen staff or fishmongers.
It may start in one nail fold but can affect several fingers. The affected nail folds are swollen and may be red and sore from time to time, often after exposure to water. The nail plate gradually becomes thickened and ridged as it grows, and may become yellow or green and brittle.
See your GP if the condition is severe. They may prescribe antibiotic creams or tablets. In some cases, they may refer you to a dermatologist (skin specialist).
It can take months for chronic paronychia to clear, and up to a year after that for your nails to return to normal. Keeping your hands dry and warm, frequently using emollient hand cream and not biting or picking your nails can help.