Both finger and toenails are usually pale pink in color, with a lighter crescent shape at the bottom of the nail known as the lunula. White spots can sometimes appear on the nail. When this happens, it is known as punctate leukonychia. There are several types of leukonychia.
 
What is leukonychia?
Total leukonychia refers to a condition where the whole nail plate is totally white in color. White spots on the nail is known as punctate leukonychia, which is a type of partial leukonychia.
 
Another type is partial leukonychia. There are three main types of partial leukonychia:

Punctate leukonychia, which presents as small white spots.
Longitudinal leukonychia, which presents as a white band down the nail.
Striate or transverse leukonychia, where one or more horizontal lines appear across the nail, parallel to the lunula. These are also sometimes called Mees lines.

 
Patches of white skin, known as leukoderma, underneath the nail can sometimes give the impression of partial leukonychia.
 
Leukonychia can be divided into two other types - true or apparent:
 
When the white spot or line is caused by damage to the nail, the condition is known as true leukonychia. With true leukonychia, the white areas remain unaffected when pressure is put on them. These areas will grow out as the nail does.
 
Apparent leukonychia occurs when the bed underneath the nail is affected. With apparent leukonychia, the nail bed affects the color of the nail plate. It will lessen or disappear under pressure and will not grow out with the nail.
Anyone can have white nails, no matter their sex, age, or ethnicity.
 
Causes
Leukonychia can be caused by a variety of different factors, depending on the type.
 
Trauma
Injury to the nail plate or the area where the nail grows from, known as the matrix, can cause damage to the nail. This type of injury is common in children and is usually the cause of white spots on the nail.
 
The types of injury that can cause this include:
 

nail biting
manicures
day-to-day nail injuries
footwear that is too small, causing abnormal pressure on the nails 

 
As a result of these injuries, the spot will grow out with the nail.
 
Poisoning and drugs
Some forms of poisoning or medication can also cause leukonychia. This cause is relatively rare and often results in transverse leukonychia.
 
Poisoning and medication that can lead to white areas on or under the nails include:
 

heavy metal poisoning from metals, such as lead and arsenic.
chemotherapy treatment for cancer, which is either given by mouth, injection, or infusion through the skin to try and kill cancer cells or stop them from dividing.
sulphonamides, a medication used for bacterial infections, such as skin infections, septicemia, and infections of the urinary tract .

 
Systemic illness
Systemic diseases can also cause white nails. If so, they are a signal that there is a problem elsewhere in the body. Again, this is rarely the cause of white spots.
 
Illnesses that can lead to white nails include:
 

iron deficiency anemia, a lack of iron in the body
liver cirrhosis, which is scarring of the liver
kidney disease
heart failure
diabetes
problems with the digestion of proteins
an excessive loss of proteins in the intestines
zinc deficiency
hyperthyroidism, an overactive thyroid resulting in abnormal levels of the thyroid hormone in the body
psoriasis
eczema 

 
Fungal disease or infection of the nail or skin disease around the nail can also cause white spots to appear.
 
Nails grow slowly. Complete regrowth for a fingernail takes between 6-9 months, while a toenail takes between 12-18 months. As a result, the presence of white spots or nails could be the sign of an injury or condition that occurred, or began, several months before.
 
Hereditary causes
In very rare cases, white nails can be a genetic condition. However, this is usually only because of the presence of rare, complex syndromes, such as:
 

Bart-Pumphrey syndrome, which involves nail problems, knuckle issues, and deafness
Buschkell-Gorlin syndrome, which involves nail problems, skin cysts and kidney stones
Bauer syndrome, which involves nail problems and skin cysts
Darier disease, which involves wart-like blemishes on various parts of the body

 
How to treat white spots on the nailsnails being clipped
Diagnosis and subsequent treatment for white spots may depend on nail clippings being sent away for study by a healthcare professional.
Treatment will depend on the cause of the white spots. If a doctor is uncertain of the cause, there are several tests that they may use to help them make a diagnosis:
 

mycology, where fungi and nail clippings are sent away for the study
nail biopsy, where a doctor removes a small piece of tissue for testing
blood test to identify if there is the presence of a systemic disease

 
There is no treatment for just white spots on their own. Those that have been caused by trauma will naturally grow out over time. If they are being caused by something other than trauma, the doctor will need to identify the cause and treat it separately.
 
If someone has any concerns over white spots on their nails, they should go and see a doctor.
 
Prevention
There are ways that a person can prevent white spots appearing again. Preventive steps include:
 

avoiding contact with irritant substances
avoiding excessive use of nail polish
cutting nails short
stopping the nails from becoming dry by using moisturizer after washing 

 
 
In most cases, white spots on the nail are not a problem and will go away in time [source]