Telangiectasias are permanently visible, dilated, superficial blood vessels, such as a capillary, an arteriole, or a venule. Telangiectasias vary in diameter, up to 1 mm, and range in color from light red to deep purple. The vessels may be linear, branching (arborizing), or spider-like in configuration. Their distribution and associated features help distinguish between different etiologic types.

Telangiectasias may be primary or occur secondary to cutaneous damage, congenital or acquired conditions, or hormonal or metabolic influences. Telangiectasias are also part of the tetrad of findings in poikiloderma, along with atrophy, hyperpigmentation, and hypopigmentation. 

The most common types of telangiectasia include facial telangiectasias and those associated with venous hypertension.

Risk factors for facial telangiectasias include aging, chronic photodamage, smoking, female sex, and light skin. Facial telangiectasias may also be a feature of rosacea. Telangiectasias are commonly seen at the nasal alar grooves. Ultraviolet (UV)-induced telangiectasias display a predominantly lateral facial distribution, most commonly involving the preauricular regions and lateral cheeks, whereas those associated with rosacea have a predominantly centrofacial distribution.

Telangiectasias may also be an early sign of venous insufficiency. These are dilated intradermal veins with a diameter less than 1 mm. They may be accompanied by reticular veins (dilated subcutaneous veins with a diameter less than 3 mm) and may accompany varicose veins (tortuous and with a diameter over 3 mm). The precise physiopathology remains unknown, although insufficient perforating veins are found in association with telangiectasias.