BECKY SMITH, a 37-year-old fashion consultant from Belleville, Ill., is a fan of all sorts of dual-use consumer products: vitamin water, camera cellphones and VCR-DVD players, to name a few. So when she recently discovered a makeup that promised to both cover her skin's imperfections and fight wrinkles, she snapped it up. ''It's an anti-aging foundation that has a light powdery texture, covers up my spots and lines, and has skin care benefits thrown in,'' Ms. Smith said, describing Fond de Teint Jeunesse du Visage, which she has been using for the last six months. The product ($48), from the French cosmetics maker Payot, contains vitamins, moisturizing agents and skin soothers not usually found in color cosmetics. ''When I travel, I don't need to pack my big jar of face cream, because my foundation already has moisturizers in it.''