Sensitive Skin (Part I)

From scalp to toes, it’s all skin. Some of it is modified (thick skin on heels, for example) some of it is thinner than in other places (scalp, eyelids). But as living tissue (except for the top layers – that’s all dead and even though it’s constantly shedding cells), it’s not inert. This post is about to the nature of the top layer of skin – and why you need to protect it.©Science-y Hair Blog 2013

A little skin architecture:©Science-y Hair Blog 2013

The Stratum corneum is the top layer of skin and if you have sensitive skin, this is the place where your efforts can make the most difference. Don’t think of it as a pile of dead skin cells – it’s way more active than that. Imagine a brick wall. The corneocytes are the bricks made of protein (lots of keratin – like hair) which can hold a lot of water. There are around a dozen layers of these, linked by proteins at the outer layer of the corneocyte and surrounded. These protein bonds are the “mortar.” Lipids and ceramides and other components from living cells below blend together to form an environment surrounding the corneocytes (around the bricks and mortar) The lipid mixture, “mortar” and the linkage between corneocytes creates a flexible, but strong layer at the top of the skin, both repelling water from outside the skin and preventing water loss from the skin. In this lipid layer is cholesterol, amino acids, triglycerides, phospholipids, glucosaminoglycans, hyaluronic acid to name a few. These linkages break and corneocytes are shed daily, but new ones take their place from beneath.

Image source and interesting reading can be found here: http://dermatology.about.com/od/anatomy/ss/sc_anatomy.htm

Within corneocytes there is “Natural Moisturizing Factor” comprised of  sodium “PCA” or a salt of pyroglutamic acid (an amino acid), lactate, urea, sugars, amino acids and other “ingredients” which prevent dehydration in these otherwise non-living cells. These compounds are water-soluble, so repeated wetting of skin can remove them. That’s why your hands get chapped and rough and cracked with too-frequent washing, you’ve damaged your skin’s barrier. This can take weeks to recover. Natural Moisturizing Factor is produced by the breaking down of a protein in skin. More NMF is produced when humidity is low, less when humidity is high - just one of many ways the skin maintains hydration.©Science-y Hair Blog 2013

In situations of skin disease like eczema, the stratum corneum is disrupted, the corneocytes are shed too rapidly and the moisture-sealing barrier is lost. With it goes it’s protection against chemicals in the outside world and therefore chemicals which might not irritate healthy skin can irritate sensitive or damaged or unhealthy skin. The skin cannot stay hydrated, so it cannot heal quickly.

Find this image source and more about allergies and skin disease here : http://www.medscape.com/viewarticle/584252_11

And I have not even mentioned the layer of oils and bacteria and the other goodies on top of your skin which add to the barrier capacity of skin! Another time perhaps…©Science-y Hair Blog 2013

So what’s the take-home message?©Science-y Hair Blog 2013

1) Skin is a very complex design and when healthy, it does an excellent job of protecting itself.

2) Skin is not designed to be wetted frequently or for prolonged periods of time and this can lead to dry, itchy skin which is more sensitive to pressure, temperature, emotions, chemicals and allergens.

3) Humectants are critical in lotions and creams because they attract moisture. Humectants are the "moisturizers" in lotions including:
glycerin
urea
sodium lactate 
hyaluronic acid
sodium PCA
amino acids 
propylene glycol (can be irritating to sensitive skin!)
oatmeal (colloidal)
Aloe vera
sorbitol
glycine betaine
caprylyl glycol
panthenol (humectant-like, skin-soothing)
niacinamide in lotions can help restore a healthy skin barrier - not specifically a humectant, but has anti-inflammatory action and stimulates ceramide and collagen production
©Science-y Hair Blog 2013

4) Oils in lotions can hold in moisture, they are "emollients" along with triglycerides, squalene, cetyl or alkyl esters and "butters" like shea butter or cocoa butter and also mineral oil and petrolatum
©Science-y Hair Blog 2013

5) You can prevent skin damage by keeping washings as infrequent and brief as possible in cool or warm, not hot water, avoiding soap and daily aggressive scrubbing (including vigorous towel-drying/rubbing).

6) For skin with eczema or dermatitis, look for creams with ceramides, humectants, and free of fragrance, herbal extracts and irritating chemicals. Apply these to skin still moist from showering, or to skin moistened with a saline solution or water.

7) Worried about being dirty? Don’t be. Agitation – rubbing hands together under water, for example, is ideal for removing “germs” and the majority of soils you need to remove. Soaps and detergents are best at removing what water cannot dissolve or rinse away, such as oils, clay or silty soil which is difficult to remove, poison ivy, proteins (think dried blood). Body odors may be better removed with detergent because of the complexity of the stink (oils, bacteria, salts and chemicals from sweat).
©Science-y Hair Blog 2013

9) Use mild cleansers (or dilute them with boiled water yourself) and follow with re-fatting via lotions or creams containing emollients (oils, fatty alcohols, petrolatum) and humectants.

Causes of dry skin: Genetic (for example, the oils on your skin do not spread easily), chlorine in tap water or swimming pools, skin disease, allergy (inhalant allergies, contact dermatitis and food allergies) UV/sunlight exposure, sunburn or chronic UV damage, exposure to solvents, acids or bases, frequent washing, and aging.

More to come on dry skin, sensitive skin, acne, eczema, atopic dermatitis and other fun things!