Hopefully, you have read my link on Using Retin-A for wrinkle reduction and are now wondering just how safe is this product. After all, Retin-A (tretinoin) is the "gold standard" for topical reduction of wrinkles and also is a powerhouse in the treatment of acne as well.
Again, Retin-A is nothing more than a form of Vitamin A that irritates the skin and cause regrowth. It literally forces your face to grow new, more "baby-like" skin. (You do have to be careful not to overapply as tretinoin can increase irritation, inflammation and sun damage if used incorrectly.)
Because Retin-A is so widely used, there has been considerable research as to its safety. Below is a summary of some of the most interesting points.
1. Hayflick Limit (Telomeres and Telomerase). One concern with tretinoin use is that it does cause your face to regenerate new skin. As your skin cells recycle, some have been concerned that eventually the skin cells would reach the point where they no longer divide easily and become dysfunction, "old" cells. In other words, does Retin-A possibly trade an improved look in one's younger years for a worse look in your older years?
This is definitely a valid question as one of the theories of aging has to do with shortened telomeres. (See my link on Telomerase and Aging for more details.) Again, as the cell divides, it loses a little bit of genetic material off its ends (telomeres) and some tissues begin to have problems at that point. However, this appears not to be an issue with Retin-A (although there has been definitive study to date). There are millions of Retin-A users and there has been no observed end-of-life accelerated aging. (Talk to your doc of course.)
One of the reasons for this may be that the Hayflick Limit does not seem to apply to skin cells (fibroblasts) that make collagen. These powerhouses have shown a Hayflick Limit in a "test tube" but humans clearly have many more cell divisions than this laboratory limit. Both telomeres and telomerase appear to be preserved virtually indefinitely. 
2. Retinoic Acid. Retinoic acid is the chemical name for Retinol, the close retinoid cousin of Retin-A, that is used in literally hundreds of skin care products for wrinkle reduction. Retinoic acid has been shown to extend the Hayflick Limit by 50% in the lab.  Again, fibroblasts do not seem to be governed by the Hayflick Limit in live human subjects, but it is comforting to note that retinoids seem to actually improve the situation.
3. Sun Damage. One protocol for those who use Retin-A is sun avoidance, because it can lead to increased risk for sun burn. Therefore, one concern is that perhaps it would accelerate photoaging and/or sun damage. A couple of studies have actually shown the exact opposite. For example, one study on mice, who were photoaged with UV lamps, documented that those treated with retinoic acid had less damage than those that were untreated.  Once again, tretinoin has been shown to actually heal.
1) Arch Gerontol Geriatr, 2002 May-Jun, 34(3):275-86, "Promise and problems in relating cellular senescence in vitro to aging in vivo"
3) Connect Tissue Res, 1984, 12(2):139-50, "Topical retinoic acid enhances the repair of ultraviolet damaged dermal connective tissue"