The skin is made up of two major layers, the dermis (the deep layer) and the epidermis (more superficial layer). The surface of the skin that we see is the epidermis. This is actually made up of 5 sublayers. The cells that we see on the surface are called keratinocytes. These cells take about one month from their formation through the entire process of maturation to get to the surface. So, skincare treatments that make actual changes in the cells themselves take about a month for what you are doing now to reach the surface so you can see it. These include Retin-A, retinols, hydroquinone, vitamin C, steroid creams (for pigmentation, for a rash works faster) and products of this nature.
However, if the skincare product that you are using produces a more immediate, and often short lived, effect of hydrating the skin you can see it much sooner. The effects of hydration should be felt right away and seen within 24 hours. However, this will go back to the way that it was as soon as you stop using it.
Depending on the ingredients, the effects of cleansers can be seen within the 24-48 hour time frame from the cleanser alone. However, if it contains other ingredients (which I like when mine do, to get a 2 for 1 effect) like glycolic acid, this may take 4 weeks to see the end result.
So, if you are unsure about how long to try skin care before making a change, use it for 4 weeks to be on the safe side. If you can’t tell a difference at that point, it may not be the right product or combination of products for you. A consultation with a dermatologist or plastic surgeon can help point you in the right direction!
Image borrowed from Hack That Life