In simple terms: 

dry skin lacks oil, dehydrated skin lacks moisture. 

Lack of oil is due to reduced sebum production linked to a disrupted synthesis of epidermal lipids. 

Dehydrated skin, on the other hand, is the result of a compromised Natural Moisturising Factor (NMF) and faster moisture loss from the stratum corneum. 

The two conditions have different causes and effects, so they need different approaches. 

It seems intuitive: skin feels dry → you give it water → problem solved. 

But skin doesn’t work that way. Its moisture doesn’t come from outside. 

The water content of the outer layer of the skin, the stratum corneum, is not determined by how much water you apply to its surface. It depends on the integrity of the lipid barrier: a layer of ceramides, fatty acids, and cholesterol in roughly a 1:1:1 ratio. When this layer is intact, the skin is able to hold on to its moisture. 

When the barrier is damaged, the skin responds by increasing lipid production, not water production. The corrective signal is lipid-based, not hydration-based. The skin does not “ask” for water — it asks for lipids.

Dry skin treated with water-based products that contain little or no lipids may feel temporarily better, but it still does not receive the materials it needs to rebuild its barrier. 

 Dry skin is a skin type that means your skin doesn’t produce enough oil (sebum). It’s the opposite of oily skin. 

The amount of sebum your skin produces depends mostly on your genes and hormones. That means if you have dry skin, you’ll probably have it for a long time. The same is true for oily skin. 

As skin ages, however, it naturally becomes drier. The ideal level of oiliness is somewhere in the middle, which we call “normal skin.” 

Sebum and epidermal lipids together form the hydrolipid film on the skin’s surface.

When their production is reduced, the barrier lets out more water than it retains, and transepidermal water loss (TEWL) increases. 

That is why dry skin needs lipids to rebuild the barrier. 

Себумът и епидермалните липиди заедно образуват хидролипидния слой на кожната повърхност. Когато производството им е намалено, бариерата пропуска повече вода, отколкото задържа и трансепидермалната загуба на вода (TEWL) се ускорява.  

Затова сухата кожа се нуждае от липиди за изграждане на бариерата. 

Is my skin dry or dehydrated?

First, work out what type of skin you have: oily or dry.

Oily skin:

• visibly oily, shiny;
• leaves greasy marks on a pillowcase enlarged pores, blackheads in the T-zone (forehead, nose, and chin) 
• prone to acne and breakouts 
• moisturisers often make the oiliness worse makeup tends to slide off and does not stay in place 

Dry skin:

• no visible oiliness or shine 
• small pores 
• feels tight and has rougher, more uneven
• patches to the touch 
• cream absorbs immediately 
• prone to cracking, flaking, redness and irritation 
• makeup settles into fine lines and skin flakes
  

Dehydration can affect any skin type, including oily skin. If oily skin also feels tight and strangely dry almost like there is a greasy layer sitting on top of plastic, it is probably dehydrated. 

Dehydrated skin is a temporary condition, not a skin type. It can happen to anyone. 

The issue here is the Natural Moisturising Factor (NMF). This is a water-attracting mix of substances inside the corneocytes that draws moisture from deeper layers of the skin and from the air. When the NMF is compromised, water does not stay in the stratum corneum, and the skin loses moisture more quickly. 

Causes:

• aggressive cleansers 
• over-cleansing and over-exfoliating 
• skincare with alcohol 
• cold or dry air; heating during winter 
• responds slowly even to rich products — requires consistent barrier-building. 
  
  

What dehydrated skin looks like:

• tight and taut instead of soft and plump 
• tired and dull can be both oily and flaky 
• fine lines appear and disappear quickly when you press skin lightly  
• responds quickly to a moisturizer — temporary relief is characteristic. 

A combination of oily and dehydrated skin is extremely common, especially in people using “sebum-control” products that remove sebum along with the NMF. 

Applying heavy greasy creams does not solve the problem, because too many lipids on the outside do not replace the damaged NMF inside the corneocytes. 

Water-based creams give only momentary relief, which is quickly cancelled out by transepidermal water loss. 

The two conditions can exist at the same time, but they come from two independent mechanisms that need different care. 

The key question: does the feeling improve quickly after applying a light humectant?

If yes, it is likely dehydration. If the skin stays dry despite hydration, it’s likely a structural lipid deficit. 

Dry skin needs lipids (fatty acids, emollients), which are found in plant oils and squalane, as well as occlusives.

Emollients strengthen the skin barrier structurally, reduce dryness, and make the skin feel smoother, softer and fuller.

Occlusives such as shea butter, cocoa butter, coconut oil and waxes form a physical barrier that literally “seals” the skin and prevents moisture loss. 

Cold-pressed plant oils contain fatty acids with a similar profile to the skin’s own natural oils. That is why the skin “recognizes” them as familiar and integrates them into the barrier instead of leaving them as just a greasy layer on the surface. 

Dehydrated skin needs humectants — glycerin, panthenol, urea, which attract water and hold it in the stratum corneum where they are applied. Their drawback is that they do not choose which water they bind. For that reason, using them carelessly without an occlusive can pull moisture out of the dermis and create the opposite of the desired effect. 

Правилната последователност е хумектант, следван от оклузив, който да “запечата” влагата и да не ѝ позволи да се изпарява толкова бързо. 

И в двата случая агресивните почистващи препарати влошават ситуацията. Те отстраняват NMF и себума едновременно и нарушават и двата механизма.