Final answer:
Repeated shampooing can affect the durability of nylon or rayon extensions, causing them to shrink or melt under high heat. Tangling is also a common issue.
Step-by-step explanation:
Repeated shampooing can affect the durability of nylon or rayon extensions. Both materials may shrink if exposed to high heat. Nylon extensions have a high melting point and are unlikely to melt, while rayon extensions have a lower melting point and may melt under high heat. However, tangling is a more common issue with repeated shampooing, as both nylon and rayon extensions can become tangled and difficult to manage.