Dehydrated skin is not a skin type as much as it is a condition of the skin. It doesn't discriminate between dry, oily, or combination skin and can be aggravated by topical skin care as much as lifestyle (binge drinking or smoking, for instance).
It's hard to describe dehydrated skin, since I feel it can present itself differently in many people. However, in my experience, it's generally skin that appears lackluster and dull, sallow or "tired," and when pulled taut, it almost seems to wrinkle a bit. Dehydrated skin doesn't "bounce back" easily and is more prone to congestion (bumps, blackheads) and acne. It generally soaks up moisturizer yet looks oily in spots and feels dry as a bone in others.
The first thing to consider, and the most obvious, is moisture content. Do you drink adequate amounts of water a day? This doesn't mean chugging water until you feel like a portable kiddie pool, but you should be drinking 4-6 glasses a day.
Another facet of moisture is how much moisture is around your skin and what is on your skin to drink that moisture up (and hold it to the skin itself). For people in drier environments or simply those of us prone to dry or dehydrated skin, I highly recommend investing in a warm mist humidifier (cold mist must be cleaned more frequently and makes a room feel clammy). I run mine virtually every night, and it makes a noticeable difference in how plump my skin remains throughout the day and night.
You also want to be paying attention to what kind of ingredients are holding moisture to your skin and how you are using them. I'm talking humectants here, such as glycerin, hyaluronic acid, and squalene.
Glycerin is easily the most recognizable and common humectant. It should never be applied straight, though a couple drops can be added to your favourite moisturizer if you feel in need of a boost. It is fairly sticky though, so I wouldn't recommend adding more than two drops. On that note, I recommend against doing this during the day, since it can make skin more "shiny" and sticky.
Glycerin is found in most skincare products and is widely available. It is also an acne trigger in a small number of people.
Hyaluronic acid is a naturally derived ingredient that can hold up to 1000 times its weight in water. It is very light, thin, and usually is not sticky. It is most commonly found in serums, but is also becoming more widely used in creams and lotions. It is best applied to damp skin (not sopping wet, but not completely patted dry either) during your water-soluable phase. If you're using it as a serum, follow it with a rich moisturizer.
Some people find hyaluronic acid drying. Your mileage may vary.
Squalene is a natural, organic compound that is usually derived from olives. It's close sister, squalane, is a hydrogenated derivative that has longer shelf life, but she has a lower cost and is therefore more profitable in cosmetic applications. People who have a sensitivity to olives or break out from topical use of olive oil should spot test products with squalene before using.
Your success with the various humectants are very individual. Some people prefer hyaluronic acid for their extra moisture while others prefer glycerin. Whatever you choose, keeping extra moisture around will allow your humectants to work to the best of their ability.
The next thing to consider when aiding dehydrated skin is your product usage. Are you using several topicals that dry or irritate skin? Some examples of irritating ingredients are:
Tea tree oil
Topical acne medications (Rx treatments, such as Aczone, Retin-a, Retin-a Micro, Differin, and Tazorac)
Sulfur topicals (such as Murad's spot treatment [3%], De la Cruz Sulfur Ointment [10%], and Queen Helene Mint Julep Mask)
If you're not using any of these ingredients but feel your skin is dehydrated, make sure you're not using a cleanser that strips the skin and makes it feel dry and tight after cleansing (prior to applying moisturizer). Your skin should never feel this way after cleansing, it is a sign of a damaged skin barrier. It should feel pleasantly fresh, not squeaky clean. Some common cleansing ingredients and products that cause dry skin in many (but not all) people:
African black soap
Plain ol' bar soap
Dr Bronner's soap
Acne cleansers, such as Neutrogena's Deep Clean Facial Cleanser or orange bar
Cleansers with SLS or SLES, such as Purpose
Drying clay masks used too frequently (such as Aztec Secret Indian Clay Mask)
If you're using an irritating non-RX product, it is advised that you use only one at a time and only once skin is healed and can tolerate it. Even anti-acne products can cause acne if they are irritating the skin and disrupting the skin barrier. Please allow at least one week for your skin to heal if you feel you've overdone it (bland moisturizer, bland cleanser, sunscreen).
If it's an RX product you're using, please contact your doctor for advice.
For those of you using a harsh cleanser (glare) or one that makes you feel dry and tight after use, I highly recommend you shelve it and try a gentle, non-sudsing cleanser, such as CeraVe Hydrating Cleanser or Cetaphil Gentle Skin Cleanser. This will cleanse the skin without stripping it of its much-needed moisture.
The most important thing with skincare is listening to your skin and working with it rather than fighting against it's nature. When skin is dehydrated and breaking out, you must treat the disease, not just the symptom. Once you have established a high-moisture, gentle regimen, and your skin has had time to heal (1-2 weeks), you may gradually begin to re-introduce potential irritants such as benzoyl peroxide or tea tree oil.
Hopefully this post has been helpful and answers questions I see many of you posing every day. Please feel free to ask questions and I will do my best to answer them!