iS Clinical Skin Products iS Clinical C-15 Serum Advance+ (1 oz.) iS Clinical C-15 Serum Advance+ is ideal for those with fine lines and wrinkles, hyperpigmentation, and sun damage. C-15 Serum Advance+ helps to smooth, repair, lighten, and protect the skin from future damage. Contains 1 fluid ounce. Directions: Apply sparingly to cleans skin, smoothing over face and neck (or as directed.) For best results, follow complete iS Clinical skincare regimen.