How fungus damages a nail
A nail plate is made of tightly packed, hardened keratin. In onychomycosis, fungi—often dermatophytes, a group that uses keratin as a nutrient—invade the plate or the tissue beneath it. They break down keratin as they spread, while irritation and disrupted nail growth add to the damage. The result can be a nail that turns yellow or white, thickens, lifts from its bed, and crumbles at the edge.
The visible nail is only part of the problem. Fungus can persist under the plate and in compacted debris, where a surface treatment may not readily reach it. A thick, lifted nail can therefore become both evidence of infection and a barrier to treatment.
Why clearing it takes time
Nails grow slowly. Even after treatment suppresses the fungus, damaged nail does not repair itself; it has to grow out and be replaced by healthy nail. Toenails can take many months to do so, and severe damage may take longer to improve visibly. Meanwhile, remaining fungus beneath the plate can continue the infection or contribute to recurrence.
Treatment choices reflect this access problem. Prescription topical medicines are applied to the nail, while oral antifungal medicines travel through the bloodstream to the nail-forming area. Oral treatment can reach a sheltered infection more effectively, but it is not appropriate for everyone and may require medical review. Since injury and conditions such as psoriasis can also discolor or thicken nails, clinicians may test a nail sample before choosing treatment. A crumbly nail is a clue—not, by itself, proof of fungus.
