Estrogen, the female sex hormone that modulates feminization, begins to play its role in a woman’s life during puberty (see sidebar). After puberty, estrogen is secreted from the ovary and is kept at a high level. Nevertheless when a woman reaches menopause, the secretion of estrogen decreases with the decline of ovary function. Insuffi cient estrogen affects a woman’s physiological functions. A drastic change of skin condition with aging is common.
It is well known that estrogen stimulates the fi broblast to make collagen and hyaluronic acid, and estrogen is thought to prevent the skin from physiological aging. In 1996, it was reported that male and female mice have different UV-sensitivity, and this difference depends on their estrogen levels. This suggested that estrogen may have an ability to prevent UV damage.
Since 1999, several researchers have reported studies on rodents whose ovaries have been removed. These reports have demonstrated an interrelation between photoaging and the decline of estrogen. Estrogen reduction accelerates photoaging. It is associated with the formation of wrinkles, as the skin’s elasticity is reduced and the 3D-structure of elastin fi bers in the dermis is disordererd. It is also associated with the decline of collagen by activation of gelatinase. Finally, estrogen affects secretion by the sebaceous glands and prolongs the life span of some cells by the restoration of telomere.
This knowledge of the relation between estrogen and skin aging suggests that insuffi cient estrogen at menopause not only induces physiological aging by reducing the biosynthesis of collagen and hyaluronic acid, but also accelerates photoaging by increasing the effects of UV damage. Therefore, estrogen is important for preventing skin aging and is signifi - cantly useful in the cosmetic fi eld. Although estrogen is quite useful in cosmetics, it is a type of steroid hormone and should be handled carefully to avoid side effects. This is why estrogen is restricted for use in cosmetics in many countries, and why safe estrogen, suitable for cosmetics, has been in demand.