Veins and particularly thread veins do not supply blood to an area but drain blood from that area, so thermocoaguation has no deleterious effect on that particular region of skin.
Thread veins called telangectasia or spider veins have many causes.
1) they may have no obvious cause but may even be hereditary.
2) due to hormonal changes...e.g pregnancy
3) but most commonly associated with varicose veins.
The two recognised treatments are a) thermo coagulation b)laser therapy.
Creams are useless.