A head Lice is an obligate ectoparasite of humans that causes head lice infestation. Head lice are wingless insects spending their entire life in the human scalp
Medical Definition of Hair loss. Hair loss: Hair loss is the thinning of hair on the scalp. ... The most common form of hair loss occurs gradually and is referred to as "androgenetic alopecia," meaning that a combination of hormones (androgens are male hormones) and heredity (genetics) is needed to develop the condition.