Let's start with the makeup of your skin. The inner most layer is the hypodermis which is where the cells are created. It is made up of nerves, large blood vessels, connective and fatty tissues. It's the layer that helps regulate your body temperature. Over time, the fatty layer decreases causing your skin to sag.
The middle layer is the dermis or corium. This layer has the blood vessels that carry oxygen and nutrients through your body while removing waste products. There is a lot of collagen in this layer and when the amount of collagen decreases, your skin develops wrinkles. Your skin loses its elasticity as you age and this layer has a lot of elastic fibers. The amount of collagen in your skin is responsible for how many fine lines and wrinkles appear in your skin. The more collagen in the dermis, the younger your skin looks.
The top layer is the epidermis. It is the thinnest layer designed to protect your other layers of skin. This layer is composed of four different layers with several different types of cells. This is the layer that sheds the older dead skin cells and the process slows down as you age and your ability to repair cuts also slows down at the same time.
In reality, new skin cells are formed at the inner most or deepest level of the epidermis and then works it way up to the top layer before flaking off. As far as how long it takes, it varies on age, skin condition, hormones, health, and stress. When you are young, around 20, the cycle can take between 14 and 21 days, while those classified as middle aged have a cycle that takes around 28 days but takes 45 to 60 days when people hit their 40's and 50's and it takes 60 to 90 days when people reach their 60's and 70's. So it is said the skin cycle averages between 5 and 6 weeks.
The length of the skin cycle is important because as we age, it gets longer and this means dead skin cells are accumulating on the outer layer. This causes sagging, fine lines, and wrinkles. In addition, bacteria can be trapped in the layer of dead cells, causing blackheads and acne. Many of the dead cells are irregularly shaped or discolored and when these are in the top layer, discoloration and spots appear.
Thus it is important to choose skin care products that encourage faster cell turnover while encouraging new cell production. So when you decide to try a new product, you need to give it a full 28 days to determine if it works because it is important to give your skin a chance to go through most or all of a skin cycle. It really takes that long. You can't decide if a product is working in less than that time and if you are a bit older, give it more time before you decide it isn't working.
So now you know more about the cycle of your skin and how long you need to try a product. Let me know what you think, I'd love to hear. Have a great day.