Will applying Vaseline after Tretinoin significantly reduce the effectiveness of the Tretinoin?

Thanks for your question. I would be concerned that Vaseline, or petroleum jelly, would be too occlusive for the entire face to use as a moisturizer. You might want to ask your aesthetician about moisturizers containing hyaluronic acid or other less-occlusive ingredients. You don't have to wait too long after applying tretinoin to use a moisturizer, 20-30 wouldn't really make a difference. Just continue to use a good quality moisturizer and sunscreen on the face in all seasons and add the moisturizer over tretinoin in winter if needed, but you might start to develop acne or little milia (cysts) or sebaceous hyperplasia with too much vaseline application on the face.