Subungual hyperkeratosis is a condition where a chalky substance may develop under the nail, creating a gap and making the nail feel uncomfortable. It can be caused by various factors, including psoriasis, fungal infections, and cosmetic products.

Regarding ingredients or materials, formaldehyde is an active ingredient in nail hardeners, and in sensitized individuals, a concentration of formaldehyde as low as 0.006% can trigger allergic contact dermatitis. Additionally, some nail products such as nail polish, nail polish removers, and artificial nails have shown to have some adverse effects through case reports and studies.

There is no information on specific ingredients or materials that can cause subungual hyperkeratosis. However, it is known that some systemic medications, such as methotrexate, cyclosporine, acitretin, and apremilast, can cause subungual hyperkeratosis as a side effect.

In summary, there is no specific information on ingredients or materials that cause subungual hyperkeratosis. However, formaldehyde in nail hardeners and some nail products have been associated with adverse effects. Additionally, some systemic medications can cause subungual hyperkeratosis as a side effect.