There are several causes of very thick or crumbling nails. They can be caused by injuries or pressure from shoes. Fungal infections are a common cause. Diabetes, psoriasis, or vascular disease are other possible causes.
Nail Fungal Infections U.S. Dermatology Partners
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What Can Be Done About A Thick and Painful Toenail? – Scott R
Understanding Thickened Nails
THICKENED NAILS
Why Our Toenails Thicken As We Age
A case of intractable, familial nail and skin thickening
Painful thickened toenails — Mackay Ingrown Toenail Clinic
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