Nail pterygium occurs due to:

Nail pterygium occurs due to skin being stretched by the nail plate, leading to an abnormal attachment of the skin to the nail. This condition can arise when the growth of the nail causes the cuticle or the surrounding skin to pull away, resulting in the skin moving up onto the nail bed or under the nail. It can be a result of trauma, chronic inflammation, or specific skin conditions. Understanding this mechanism is essential for nail technicians, as it can help in educating clients on proper nail care and the importance of not causing undue stress or damage to the nail and surrounding tissues.

The other choices do not accurately explain the cause of nail pterygium. Biting nails primarily leads to issues like infection or shape alteration rather than pterygium. Nail surface damage doesn't directly relate to the condition in question but can affect the overall health of the nails. Age-related changes may influence nail appearance or texture, but they do not specifically cause pterygium.