Dehydrated skin is not dry skin. Dehydrated is a skin condition lacking water, whereas dry skin is a skin type lacking oil. Any skin type can become dehydrated, even oily skin. My oily skin is currently a bit dehydrated , because of acne treatment gel. I decrease use to once a day or every other day depending on how dehydrated my skin becomes. I also drink a TON of water and no soda. Oily skin must be hydrated and moisturized, whether dehydrated or not. Skin can also become dehydrated from sweating, not drinking water, dry weather, not moisturizing, skin treatments, alkaline based products, and medications.
Dehydrated skin looks flaky and can feel tight and dry. It will also absorb products extremely fast, so layering on moisture throughout the day is a good idea. If you wear a makeup base, your skin will absorb the base, your skin will feel tight and your face may look like it will "crack". Adding that extra moisture is very important to prevent this and keep skin hydrated. If you are acne prone, dehydrated skin can actually worsen your condition, so drink plenty of water and don't forget a light moisturizer like CeraVe Moisturizing Lotion. This lotion contains ceramides, which helps moisturize, soften skin and retain water. Cetaphil Moisturizer is also a favorite of mine.