Melanogenesis is a defensive mechanism our skin uses to protect it from too much sun exposure. It is characterized by production of melanin, which are transferred to the keratinocytes, producing darkened skin. In darker skinned people, the melanin breaks down more slowly than in light skinned people. (We generally call this a tan or freckling...)
There is another type of pigmented skin type - those with vitiligo. The body's immune system attacks the melanin and leaves the skin unpigmented. The treatment for this? Wear lots and lots of lots of sunscreen or clothing when outside, and avoid direct sunlight. You can't tan those areas, so you just end up with darker skin around the white patches, so the only thing to do if you want to hide them is to use a coloured foundation. (If you don't know this already, my husband has vitiligo. He has huge white streaks through his hair and beard, with quite a number of white eye lashes. He's very pale, so it looks good on him.) This can be a very difficult condition for those who have anything but very pale skin. This is definitely something you want to discuss with your doctor.
Usually having a tan isn't an issue - unless you've gone all orange from fake tanning, and you're on your own there! - but having age spots can be. These are light brown to black spots found on the parts of our bodies that have had a great deal of sun exposure. The melanin is produced, but doesn't go away. This is a problem for those of us over 40, as our skin can't regenerate quickly after sun exposure. The age spot is a symptom of too much sun exposure and not enough regeneration. It isn't generally a medical problem, but it can mask skin cancer in rare cases.
You can use ingredients that inhibit tyrosine to treat these problems. (Tyrosine is a key component of melanin production). Such ingredients include hydroquinone, arbutin, Vitamin C, kojic acid, mulberry extract, or liquorice extract. You can also use something like niacinamide, a derivative of Vitamin B3 that can hinder the melanin from being transferred to the keratinocytes.
I cannot suggest how to incorporate these ingredients into your products because you really need to study up before using them. I suggest finding a product you like with one of these ingredients, then seeing how your skin reacts and the level used in said product before formulating your own.
You can also use exfoliating products to help with overpigmented skin. If you can get the cell turnover rate on your skin to increase faster than the production of melanin, then you will see a lessening of those spots. You can use AHA or salicylic acid in your products, or you can use mechanical exfoliation in the form of a washcloth, light brush, or clay or jojoba beads (or other light exfoliants) in your products.
If you are in the non-pigmented category, stay there by using lots of sunscreen, wearing hats or protective clothing, and avoiding direct sunlight. In fact, stay out of the sun: Stay home and play video games, play in your workshop, and enjoy some TV. (Okay, that last sentence probably isn't the best advice.)
Join me tomorrow for the last of the categories - wrinkled (W) or tight (T) skin.