The risks of spider vein treatments are relatively low.  There is a risk of skin color change both hyper-pigmentation (darkening & usually temporary) and hypo-pigmentation (lightening & can be permanent).  This risk is minimized by using different types of lasers for different skin color types as well as experience in proper use of these devices.  There is a small risk of burns and blistering which can lead to scarring.  Again, customizing the treatment to match the skin type minimizes these risks. This is why Dr. Rubinstein uses 3 different types of laser modalities.  Larger spider veins can sometimes leave a void after treatment creating a skin indentation which will improve over time but may require other treatment modalities if they persist including resurfacing lasers and or dermal fillers.