Which type of hair has the smallest diameter and is more susceptible to damage?

Fine hair has the smallest diameter compared to other hair types, which typically include coarse and medium hair. Because of its thinner structure, fine hair is inherently more delicate and prone to damage. Factors such as chemical treatments, heat styling, and environmental stressors can have a more significant impact on fine hair, leading to issues such as breakage, split ends, and overall weakness.

In contrast, coarse hair, with its larger diameter, tends to be stronger and more resilient to damage, making it less susceptible to the same degree of harm. Medium hair strikes a balance between the two, having more strength than fine hair but still being more fragile than coarse hair. Thick hair generally refers to either a high number of strands or a coarse texture, both of which contribute to a more robust structure overall.