A hormone involved in the development of secondary sexual characteristics in the female, and regulation of the menstrual cycle. There are many different types of oestrogen (e.g. oestradiol and oestriol), but they are all known collectively as the oestrogens. Oestrogens are found in both males and females. In females they are made in the ovaries and in males they are made in the testes (albeit in small amounts). They are also made in the adrenal gland in both sexes. Although the levels of oestrogen remain constant in males, they fluctuate in females depending on the phase of their menstrual cycle. Oestrogen has many physical effects on the body (e.g. it affects the balance of cholesterol in the blood), but it also has psychological effects, for example, oestrogen levels can affect how a person feels emotionally.