Hi Carl E.
People who are lactose intolerant do not produce the enzyme lactase that breaks down milk sugar and therefore experience discomfort at different levels of lactose intake. Yogurt contains the enzyme lactase and therefore can be tolerated by many who are lactose intolerant. Yogurt is not really lactose free but has very low lactose content. Unfortunately many new commercial brands have higher lactose content, as they are often added milk solids. Which ones are tolerated and how much, is highly individual, so what works for somebody else might not work as well for you. Test for yourself, and write down the amount and brand. Make sure you only test one product at the time.
With kind regards Iris Daniela Classon