Hair thickness is largely hereditary and depends on factors like age, the presence of any health condition that is affecting hair health, hormonal imbalance, nutritional deficiencies, and the use of harsh chemicals like dyes and heat styling tools.
Hair thickness also generally varies according to ethnic groups. A study conducted showed that individuals with Asian ancestry had a larger hair diameter than those of African or Caucasian descent (1). Apart from the presence of specific genes, hair care practices followed by individuals or traditional practices followed by ethnic groups may be the cause behind this variation.