Answer:
Trans retinoic acid or Retin A is thought to have hormone like properties such as modification of the immune system increase in collagen synthesis, etc. It does work but it is a potent teratogen. It is usually given in the form of a 0.05% cream at night to treat effects of photoaging. It is current practice to give it before a peel to de-keratinize the skin allowing deeper and more even penetration of the agent.