What causes sm red dots on lower legs?

Dots. This can't be diagnosed with the information that is available. A history, physical examination & other studies may be needed to determine cause/causes.
Visual DX. Hi, it’s hard to say without a picture but there is a great app that may be able to help you get a diagnosis without being seen in person by a dermatologist. The app is called VisualDX and is one of the best, if not the best out there. Many clinicians, including myself, use it. Just snap a photo and it gives you a list of possible diagnoses. Good luck!