Spider naevi are due to action of -
The vascular spider, aerial spider or spider angioma or naevus is the most classical vascular lesion that is sometimes a presenting sign of chronic liver disease. Spider telangietasia occur in up to 10-15% of normal individuals and may also be seen in pregnant women (3rd trimester).They may also be seen in thyrotoxicosis, patients with rheumatoid ahritis, receiving estrogen therapy and women on oral contraceptives. In adults, spider nevi are usually seen over the face, neck, and upper pa of the trunk, and arms (vascular territory of the superior vena cava). It is unusual to find them below a line joining the nipples. They vary in size from 1 to 2 mm in diameter. It comprises a central aeriole represented by a red point from which numerous, small, twisted vessels radiate. Application of pressure on the central aeriole with the head of a pin or a match stick causes blanching of the whole lesion. Vascular spiders have been attributed to excessive levels of estrogen which cause blood vessels to enlarge and dilate. The presence of spider nevi is accompanied by an increased serum estradiol/free testosterone ratio in male cirrhotics. Reference : page 943 Davidson's Principles and practice of Medicine 22nd edition
Estrogen
Androgen
Steroids
Progesterone
Endocrinology