SHBG (Sex Hormone-Binding Globulin) is a type of protein produced mainly by the liver and released into the bloodstream. The primary role of SHBG is to bind to the Sex Hormones Testosterone and Oestrogen and transport them in the blood in an inactive form. Testosterone and Oestrogen can be found in both men and women, but at different levels. For example, in men, about 45% of testosterone is tightly bound to SHGB and in women about 70%. These gender differences in binding of SHBG and other proteins to the sex hormones in the bloodstream accounts for male and female characteristics. Slight changes from normal levels of SHBG and therefore Sex Hormones can cause certain symptoms. In adult men, it is usually decreased testosterone that causes symptoms and SHBG levels can be used to discover the reason for a decrease in libido (sex drive) and erectile dysfunction. In women, even slight increases in testosterone can cause symptoms such as amenorrhoea (the absence of monthly periods), infertility, acne and hirsutism (increased hairiness).