4 Answers

I its deficiency in zink I think and could mean that there is another deficiency maybe iron get your Doctor to check it out

Psoriasis is a chronic skin condition marked by inflammation, redness, itching and even lesions of the skin. PLAQUE psoriasis is the most common form. Other types of psoriasis are nail (affecting FINGER AND TOE NAILS), scalp, guttate (small sores on torso, arms, legs and scalp), inverse (forms in folds such as armpits, under breasts and in the groin), pustular (marked by pus-filled blisters) and the rare erythrodermis (a peeling rash over the entire body). Psoriasis can change from one type to another, or in some cases a person may have more than one type at the same time.

It depends where the white appears - under nail on feet or fingernails especially around the cuticle areas can be fungal infection - See your Doctor or Pharmacist there are creams for this and in more serious cases tablets which are strong and have side effects if taken for too long. If the white areas are on the toes - a chiropodist would help you. 

If there are only a few nails affected with white spots, it could be mild trauma to your nails. If all of tem are affected with streaks and white spots, it could be a more serious condition, like anemia ,diabetes and so on. See a doctor, if that is the case.