Yellow nails are often caused by a fungal infection, especially if the nails become thick, brittle, or start to crumble. But sometimes yellow nails can be a sign of more serious health issues like lung disease, diabetes, or thyroid problems.
What to watch for:
Yellow or yellowish-green nails
Thickened or crumbly nails
Nails growing slowly or separating from the nail bed
Possible causes:
Fungal nail infection
Lung diseases such as chronic bronchitis
Diabetes or thyroid problems
Nail psoriasis