The hardening and shrinking that occurs around the hair follicle stunts hair growth. You can compare this to a large plant growing in a small pot.
Hair tries to grow as normal but due to hair follicle hardening, it can only grow a few millimeters.
This is not true. Such hair is in fact the first to disappear. Once the short hair starts to grow back, your hair count increases. A strand of hair, which previously had a thickened collagen structure, develops a thinner structure. A normal hair is approximately 0,06 mm thick.