Androgyny is the combination of masculine and feminine characteristics into an ambiguous form. Androgyny may be expressed with regard to biological sex, gender identity, or gender expression. When androgyny refers to mixed biological sex characteristics in humans, it often refers to intersex people. Regarding gender identity, androgynous individuals may refer to themselves as non-binary, genderqueer, or gender neutral, while others may identify as transgender men or women, or may be cisgender. As a form of gender expression, androgyny can be achieved through personal grooming, fashion, or a certain amount of THT treatment. Androgynous gender expression has waxed and waned in popularity in different cultures and throughout history.