What is the best OTC treatment for aging skin on hands and arms?

Unfortunately there is no effective OTC product for your problem.  OTC products are not made strong enough, and or don't have the correct percentages of active ingredients to actually do much good.  It sounds as if you need a good, high quality moisturizer PLUS sunscreen.  You may want to consider having a peel done on your hands to get the dry, dead skin off so that an effective moisturizer can actually penetrate deep enough to re-hydrate your hands.  Then SPF of 40 with broad spectrum coverage will be a great help.

Our office specializes in age spot removal and we begin with topical application of Melarase creams, followed by Melapeels and laser treatment. Best, DR. Karamanoukian Los Angeles

Thank you for your question about age spots treatment. Pictures would be helpful.I do not know of any OTC treatments that will be effective.In general, these treatments could have a role and may or may not be helpful for you:5 FUAldara CreamIntense Pulsed LightBroad Band LightTo be sure what (if any) treatment is appropriate for you, see two or more licensed and board-certified providers in your area for a complete evaluation to make sure you are a good candidate and that it is safe for you to have these treatments.I hope this helps.Best wishes.

Sunscreen and sun protection are most important. A high quality medical skin care regimen (see below) can also be very helpful, Consult a board certified Dermatologist or Plastic Surgeon for proper advice.

There is NO OTC effective treatment for significantly sun damaged skin as you describe. To effectively thicken and rejuvenate the skin requires prescriptive medications such as Retin-A or other physician administered treatments. See a physician specializing in skin rejuvenation. There is, however, one thing OTC that you can do to prevent significant further sun damage. That is to use a sun block containing 6-12% clear Zinc Oxide DAILY. The sun damage is from UVA, not from UVB that most sun screens block. UVB is also strongest midday, down south in the summer whereas UVA is about the same all day all year and at all latitudes. Other UVA sun blocks last only an hour. The zinc oxide requires reapplication whenever it is washed or rubbed off.