Many people confuse dry and dehydrated skin. They both need different care.
Dryness is a skin type. If you have dry skin your skin lacks oils and it is characterised by small pores and you require oil-based products.
Skin dehydration is a skin condition, your skin lacks water. It's caused by climate, diet or harsh products. Treat with products that bind water to the skin (humectants) like glycerine or hydraulic acid.