Thank you for your question.
The most common side effect from spider vein treatment is hyperpigmentation or hypopigmentation of the skin at the treatment sites (spots that look lighter or darker than the adjacent non-treated skin). This is usually the result of the heat energy from the laser damaging or burning the skin. With sclerotherapy injections it is either the result of hemosiderin pigment from blood cells getting trapped in the skin or under the skin, or from inflammation of the skin as a result of the chemical reaction that results from the sclerotherapy medication. These are unfortunate and often unavoidable side effects . . . the skin is intimately associated with the veins. When heat or chemical is applied to the veins, the skin is at risk for a reaction as well. The skin side effects that occur from sclerotherapy will usually resolve and fade over time. But the thermal skin side effects from laser are usually permanent. For that reason, I recommend sclerotherapy over laser therapy whenever possible. But there definitely are circumstances in which thermal treatment with heat is preferred (for example, on the face and on the ankles). For spider veins that are better served with thermal energy (over sclerotherapy) due to their location, I actually prefer the use of Ohmic thermolysis with the VeinGogh or Veinwave device rather than laser whenever possible. I have found this technology to have less risk of permanent skin damage or thermal burns that leave scars. In addition, the VeinGogh / Veinwave devices are FDA approved for spider vein treatments, as they have been shown to be safe and effective with low risk. I have found Ohmic thermolysis / thermocoagulation to be very effective on the face, legs, and ankles and have also found it to be of lower risk than the laser treatments. I see patients on a weekly basis that were unhappy with their results with laser for spider veins.
My recommendation to you would be that you go see a board certified vein specialist who is a MD, rather than going to the local med spa. The level of training of the individual performing the procedure is of utmost importance in terms of you getting the results you are looking for. Vein specialists can usually offer all of the various treatments and recommend the one that is best for your individual skin type and circumstances.
I hope that this information was useful to you.