Air bubbles in the nail, warts, fungus, psoriasis, and eczema can cause leukonchia. They can be a sign of sarcoidosis which is a disease that affects the skin, lungs, and other organs.
For this reason if you have an issue like this you must not ignore it and should go to see your doctor. They can be formed because of minor injuries to the base of the nail.
Moreover, they can indicate kidney disease, heart failure, liver cirrhosis, inter alia, and irregular diet. They are mostly inflammatory responses to an infection or injury.
If in case you notice changes on your nails which are not usual or are unfamiliar to you, then you better consult your doctor.