The present invention generally relates to compositions and methods for topical or transdermal delivery, treatment of skin, and improving the appearance of skin, e.g., medically or cosmetically. In some cases, the composition may include nitric oxide and/or peptides such as thyrotropin-releasing hormone (TRH) and/or GnRH (gonadotropin-releasing hormone). The nitric oxide and/or peptide may be present within a first phase comprising a lecithin, such as phosphatidylcholine. In certain embodiments, the lecithin is present in liposomes, micelles, or other structures containing nitric oxide, peptides, or both. The composition can take the form of a gel, a cream, a lotion, an ointment, a solution, a solid “stick,” etc., that can be rubbed or sprayed onto the skin. Other aspects of the present invention are generally directed to methods of making or using such compositions, methods of promoting such compositions, kits including such compositions, or the like.