Since I don't know what paint, varnish or stain may be on the risers, it's impossible for me to say. If there is varnish, you need to strip it, because nothing will adhere to it, and all your efforts will wipe right off. To be safe, after sanding them, use a very good quality primer paint (not water based) that is designed to adhere to anything. The fumes are toxic, so you need good ventilation. Don't do this if you're pregnant. Use a fan and a filtered mask (not a paper dust mask), and of course serious gloves. After that has dried for a day, you can paint with acrylic paint on it.

Thank you for your tips. The stairs used to have carpet on them. It was gold shag from the 70s. we tore it out and it was quite an experience. A carpet installer here in town advised us that the jute backing had deteriorated and the chemical smell and breakout on my husband's arms was the result. So it has been bare for quite a while and we are repairing/sealing gaps to make it a presentable staircase. So, it has never had a finish on it... just the spatters, etc., when the upstairs was added to the house in 1973. Here's a couple of pics to give you a better idea. Thanks again for your help!