Understanding Dehydrated and Dry Skin: Mechanisms, Causes and Solutions

Find out all about dehydrated skin, its causes, symptoms and best practices for effective treatment and prevention. 

Understanding Skin Dehydration

Structure and functions of the skin

It is made up of five layers:

1. The basal layer (or stratum basale): located just above the dermis junction, it comprises basal keratinocytes. They divide constantly to generate new cells, which migrate to the upper layers.

 2. The spinous layer (or stratum spinosum): The keratinocytes that migrate from the basal layer become flatter and produce more keratin, a fibrous protein that reinforces the skin's structure.

3. The granular layer (or stratum granulosum): The keratinocytes begin to flatten and produce a protein that helps form a hydrophobic barrier (which repels water) in the upper layers of the epidermis. This layer is essential in waterproofing the skin and preventing excessive water loss.

4. The lucent layer (or stratum lucidum): This layer is present only in areas where the skin is thickened (palms of the hands, soles of the feet) and offers additional protection.

5. The stratum corneum: This is the outermost layer of the epidermis, acting as a physical and chemical barrier against environmental aggression. Corneocytes are cells without a nucleus, mainly made up of keratin. 

Mechanisms of Skin Hydration² ⁵

All the layers of the skin must remain hydrated to keep it supple and elastic. In particular, the stratum corneum must contain between 10% and 15% water. The skin regulates its hydration thanks to two types of water, static and dynamic:

• Static water is retained in the upper layers of the skin, especially in the stratum corneum. It is bound by natural moisturising factors (NMFs) that attract and retain water. These NMFs, composed of amino acids and other moisturising elements such as urea and lactic acid, keep the skin hydrated, supple and elastic.
• Dynamic water moves from the deeper layers to the skin's surface and evaporates into the air. This process, known as trans-epidermal water loss, helps to regulate body temperature.
  
  It depends on aquaporin 3, a cellular channel made of proteins that facilitates the transport of glycerol and water across cell membranes to the epidermis. As a humectant, glycerol attracts and retains water in the upper layers of the skin, helping to keep it hydrated.
  Trans-epidermal water loss depends on the integrity of the skin barrier. This loss increases if this barrier is damaged or disrupted, as in dry skin or dermatological diseases. The amount of water that evaporates also depends on environmental conditions, such as humidity and temperature. Intercellular lipids in the stratum corneum also control this dynamic water by trapping it and slowing down its evaporation.
   
• Interaction between the two: A balance between static and dynamic water is crucial to maintaining healthy skin. Therefore, skincare aimed at optimising hydration must support both the maintenance of static water by NMFs and the regulation of dynamic water by a healthy lipid barrier.
   

Definition of Cutaneous Dehydration³ ⁴

In medicine, dehydration occurs when the body loses more water than it absorbs. This loss can happen through various pathways, including the skin, lungs, kidneys, and digestive tract, and is exacerbated by insufficient water intake compared with the water lost³.

Dehydration has harmful consequences for the whole body, including³: 
- Digestive tract: A lack of hydration can lead to constipation, as water is essential for helping food move through the intestines. 
- Kidneys and urinary system: Dehydration can increase the risk of urinary tract infections and lead to poor kidney function, ultimately contributing to kidney failure.
- Cardiovascular system: Lack of water reduces blood volume, leading to hypotension.
- Skin: Dehydration makes the skin dry and less elastic, compromising its protective barrier function against external aggression.

Dehydrated skin is, therefore, skin that lacks water. It occurs when the amount of water lost by the skin exceeds the amount of water that is replenished, for example, through internal hydration ortopical moisturisers⁴.

Causes of skin dehydration
 

The difference between dry and dehydrated skin

"Dry skin" and "dehydrated skin" are often used interchangeably in everyday language, yet they describe two different skin conditions.

Dry skin, or cutaneous xerosis, is characterised by a lipid deficit in the cutaneous epidermis or by a lipid, associated hydrophilic substances (natural moisturising factors or NMFs) and water⁵ deficit.

In contrast, dehydrated skin is mainly due to a lack of water in the epidermis, resulting from a loss of body water that exceeds water intake. Skin dehydration is a sign of global dehydration, reflecting an overall water imbalance⁴.

Environmental factors and skin dehydration³ ⁵

Many external factors can aggravate the signs of skin dehydration:

• Excessive sweating: In hot weather and during prolonged physical exercise.
• Abundant diarrhoea and vomiting: Particularly during acute gastroenteritis and food poisoning.
• Medication: Particularly laxatives and diuretics.
• Excessive alcohol consumption.
• Climate: Cold weather reduces humidity and dries out the skin.
• Exposure to the sun: Sun and heat dry out the skin. Ultraviolet (UV) rays penetrate the epidermis and break down collagen and elastin in the dermis. 

Impact of lifestyle habits on dehydrated skin³ ⁵

Internal factors and unsuitable lifestyle habits can aggravate skin dehydration:

• Insufficient water intake causes overall dehydration.
• Heating and air conditioning systems reduce the humidity of the ambient air, leading to skin dehydration.
• Frequent showering or bathing, especially in hot water and for long periods, can alter the skin's lipid barrier and worsen dehydration.
• Many cleansing products, such as soaps and detergents, remove lipids and water from the skin, leading to dehydration. 

Prevention and treatments for dehydrated skin
 

Prevention of cutaneous dehydration

There are several steps you can take every day to prevent skin dehydration. Adequate internal hydration is crucial; drinking enough water daily (two litres) is recommended, especially in intense heat or during prolonged physical exercise. Avoid excessive alcohol consumption, which can accelerate hydration loss.³ ⁶

To preserve the skin barrier and soothe signs of dehydration, limit the frequency of baths and showers, use lukewarm rather than hot water, and avoid over-drying. Opt for gentle, non-alkaline cleansers with a pH close to the skin's. A regular moisturising skincare routine significantly improves skin hydration, especially when these moisturising products are applied to damp skin after bathing.⁵

Finally, clothing that is too tight and irritating textiles such as wool and synthetics should be avoided. Using humidifiers at home, especially in winter, can help keep the skin well-hydrated.⁵
 

References  

1. Agarwal S, Krishnamurthy K. Histology, Skin. [Updated 2023 May 1]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537325/

2. Pons-Guiraud A. Dry skin in dermatology: a complex physiopathology. J Eur Acad Dermatol Venereol. 2007 Sep ;21 Suppl. 2:1-4.

3. Taylor K, Jones EB. Adult Dehydration. [Updated 2022 Oct 3]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK555956/

4. Eda N and al. Changes in the skin characteristics associated with dehydration and rehydration. Eur J Sport Sci. 2023 Apr;23(4):552-560.