Retinoids are one of the most popular cosmeceuticals you can buy. They are all cousins of Vitamin A, and help in growth and development of many tissues, but for our purposes just know that it helps your skin to behave like healthy, young skin.
In nature Vitamin A has 3 forms (retinol, retinal/"retinaldehyde" and retinoic acid), and they can interchange via different chemical reactions. Tretinoin is often found as an ingredient, this is a slight different conformation of retinoic acid. The "strength" of retinoids depends on their ability to then interact with the appropriate receptors which then result in the retinoid effects. Different retinoids are attracted to the receptors in different strengths, and for the "natural" retinoids this strength increases from retinol to retinaldehyde to retinoic acid.
It can take >12 weeks to see any initial improvement in the skin with retinoid treatment, maximal effects won't be seen until 6-9 months. The best improvements are seen in skin roughness, hyperpigmentation and fine lines, but you will see some improvements in coarse wrinkles and freckles as well.
There are 2 ways which Vitamin A functions:
1. Antioxidants: Protection of tissues from damage from oxygen scavengers
2. Gene Activation: Retinoids can "turn on" a cell's DNA to produce certain things, such as increase cell production or increase production of a product like collagen or hyaluronic acid (which they do!)
3. Depigmentation: Retinoids help with hyperpigmentation via a few ways. The first way is that by increasing cell turnover, they increase shedding of skin cells that have accumulated too much melanin. They also interfere with melanocyte-keratinocyte pigment transfer (in otherwords, help prevent other skin cells from accumulating too much melanin) and help disperse melanosomes.
The net result of these mechanisms is that the epidermis thickens, cells increase in their turnover and the number of cells that produce sebum decrease. There are even changes in the anchoring tissues around the skin cells, making everything more stable. Atrophy of the epidermis is reduced, more collagen is made and hyperpigmentation is decreased.
It is important to note that the retinoid you use needs to be stable in the form you bought it, and active. There are a lot of different forms of retinoids, but they can be easily inactivated in certain creams/gels and with exposure to the sun. So, look for a retinoid that comes in a package that doesn't let in sunlight. As well, your packaging should be air tight to prevent oxidation and inactivation.
Another concern that many have regarding use of Retinoids is combination with other products. While it is true that Retinoids are less stable when in the same product as some ingredients (such as Alpha-Hydroxy Acids), there should be no issues with combining them on your face. In fact, many dermatologists suggest that using both will improve the efficacy of the the retinoid as it will be able to penetrate your skin more easily. If you're concerned about applying them on your face at the same time, try spacing out products by a few minutes.
In addition, many suggest applying retinoids at night. I was unable to find any evidence that they work better at night versus morning. However, they should be started slowly (a few times a week) and increased in frequency as your skin is able to handle them. Don't be surprised if you have some redness, peeling or even stinging with use. These problems will decrease with time, allowing you to increase your use of the product.
One final note: Retinoids will have side effects. The main issue will be skin irritation, with dryness, scaling of the skin and even redness. This is especially true with higher concentrations or more effective forms. You can combat this by decreasing your use of the retinoid, think using it once a day instead of twice or switching to an every other day or even every third day schedule. Let your skin tell you what it can handle. As well, something called "paradoxical hyperpigmentation" has been described. This basically means that even though most people see improvement in skin color with less hyperpigmentation and a more even tone, there are some that will see instead increased pigmentation. If you see this, you should probably discontinue use.
Most importantly: Retinoids will make your skin more sensitive to the sun! This makes your daily use of a broad spectrum sunscreen even more important!
Updated on 4/3/2010