How long does it take for a serum or cream to begin to work and show a difference in my skin? How will I know it is actually working and worth the money?
The answer depends on a few key factors. First, what type of skin condition are you treating? If you are using serums and/or creams to control oil secretion, repair blemishes, superficial dehydration, the results will be visible much quicker, and in some cases instantly. The repeated use will eventually bring the condition under control. If you are using skin care products to address deeper concerns such as aging, (deep dehydration, lines, lack of elasticity, asphyxiation), you must allow time for these products to work. The general rule is 3 to 4 weeks while allowing for cell turnover in the epidermis. You will certainly notice some more immediate changes, . . . improved hydration, less redness of the skin, and improved vitality.
It is also very important to consider what else you are doing that influences your skin. For instance, not keeping an oily skin hydrated triggers more oil secretion, smoking contributes to asphyxiation of the skin, tanning contributes to photodamage, using products to treat hyperpigmentation, and exposing the area to UV will not give you the results you are after, (not to mention the effects of diet and stress).
A big part of using skin care products is to prevent further damage and prevention is very hard to see. You know what they say about an ounce of prevention.