In spider nevi, dilatation of blood vessels is due to

Nevus araneus, also known as spider angioma or spider nevus, is a common benign vascular lesion present in 10-15% of healthy adults and young children. They may appear as solitary or multiple lesions. In paicular, when multiple lesions are present, liver disease, estrogen therapy, and thyrotoxicosis should be considered. The name stems from its physical appearance, which is characterized by a central red aeriole, or punctum, representing the body of the spider, surrounded by a radial pattern of thin-walled capillaries, resembling legs