There are 2 types of inflammation. Acute inflammation (cuts, scratches and so forth) and chronic inflammation (when response lingers far longer than it should be).
DHT is converted from testosterone in your sebaceous gland and are mediated by binding to the androgen receptor. Combining that with a bad diet high in cholesterol results with a higher sebum production, therefore gland is enlarging. As it gets bigger over the years basically there isn't enough space for hair follicle. Like it wasn't enough persistent inflammation results with calcification and fibrosis, which is why it is much easier to prevent then to regrow.
Itch and dandruff is a strong signal of chronic inflammation. Most people just use targeted shampoo's, but it only fights symptoms not the cause. Even when scalp appears healthy after shower, inflammation persists. Acne scars are a common example of inflammation and as we can see in the studies, dermarolling helps immensely triggering healing response through acute wounding and combat chronic inflammation.