Possible causes of the nail becoming yellow are listed below.

External substances

  • Tabaco
  • Nail hardener
  • Nail lacquer

Drugs

  • Tetracycline
  • D- penicillamine
  • Vitamin D3

Skin disease

  • Psoriasis
  • Pustulosis palmoplantaris
  • Alopecia areata
  • Fungus infection
  • Trichophytosis
  • Onycholysis

Systemic disease

  • Bile secretion disability
  • Lung and heart diseases (Causes the skin below the nail to swell and disrupt blood flow)
  • Hypometabolism
  • Lympathic problems
  • Internal diseases
  • Diseases of the Bronchi and lungs
  • Thyroid disease
  • Carotenosis
  • Yellow-nail syndrome
  • Diabetes
  • Heart failure
  • Hyperbilirubinemia
  • Amyloidosis
  • Sjogren’s syndrome
  • AIDs

Any of these diseases are conditions which cannot be taken lightly. It’s recommended to visit a medical professional.