Spider or thread veins are the thread like, red coloured veins most often seen on the surface of the skin. They are not as painful as enlarged varicose veins but they are still liable to bleed and worsen without treatment.
Spider veins occur most commonly in the legs but are often seen in the face and elsewhere. These spider veins, medically referred to as telangectasias, will not worsen to the point where they will ever become the large bulging varicose veins.
If you have thread veins on the leg we always recommend that you have a Duplex scan to check there is not an underlying problem (e.g. leg pump failure).