Artificial nails can definitely make a nail fungus worse by entrapping the fungus in a closed space. It is very unusual for an infant who is otherwise healthy to have nail fungus. Your client would benefit from being evaluated by a dermatologist to confirm that she has fungus. She may, for example, have separation of the nail from the underlying bed (onycholysis), which often results in secondary issues such as fungus, yeast, or bacteria growing beneath the nail. The first step is for her to have an accurate diagnosis.
— Dana Stern, M.D. is a board-certified dermatologist specializing in nails. She works in private practice in New York City.