The dermis is by far the thickest and strongest layer of the skin. It contains collagen that gives the skin strength, and elastin, which allows the skin to recoil.  The skin thickness depends on the thickness of the dermis.  In eyelid skin, the dermis is very thin and on the back, the dermis is very thick. 

    The dermis also holds sensory nerve endings, sweat glands, and a sebaceous hair follicle system that produces naturally occurring sebum (the oil of the skin). 

    What you see when you look at your skin is the dead keratin layer.  This can vary in quality.  With age, the keratin layer becomes thick, clumpy, and irregular giving a rough, flaky, and dull appearance to the skin.  The keratin layer can vary dramatically.  The soles of the feet contain a very thick layer of keratin whereas the eyelid skin has a very thin layer.  

   The skin is very active.  Not only does the skin’s epidermis serve as a barrier, but it also has sensory input through touch and feel.  It has an immune response function and, with the help of sunlight, produces Vitamin D.  More importantly, however, the skin offers protection from ultra-violet radiation through the process of tanning.   When ultra-violet radiation penetrates into the bottom layer of the epidermis where the melanocytes or pigment producing cells exist, the radiation stimulates the melanocytes to produce melanin pigment creating the tan. 

Photo-aging and the Sun

   Photo aging is the process of accelerated aging caused from sun exposure.  The skin becomes dry and coarsely wrinkled, which gives a leathery appearance to the face.  

Ultra-violet Radiation

   The sun’s rays contain infrared radiation, visible light, and ultra-violet radiation.  The ultra-violet radiation spectrum can be divided into three types:  top

UVC:  200-290 nm wavelength
UVB:  290-320 nm wavelength
UVA:  320-400 nm wavelength

   We are lucky that UVC only reaches the earth in minute quantities, as these rays are very damaging to the skin.  UVC are absorbed by the earth’s ozone layer.  UVB is primarily responsible for tanning, burning, skin cancer, and photo aging.  However, UVA, which has the longest wavelength, can penetrate glass, augment tanning, and penetrate the dermis further than UVB.  This quality plays a considerable role in the wrinkling and sagging of the dermal layer of skin.  UVA is thought to cause cataracts.  It is the UVA that triggers drug photosensitivity and is thought to be a stronger source for skin cancer than UVB.

   There are many drugs that cause photosensitivity or a red rash from sun exposure.  These drugs react with UVA.  Of the drugs used in the treatment of acne, Vibramycin is the most reactive, followed by Tetracycline, and Minocycline (Minocin) respectively. Non-steroidal anti-inflammatory drugs such as Anaprox, Naprosyn, and Voltaren can cause photosensitivity. Thiazides, diuretics, and retinoic acid cream can cause drug induced sun sensitivity. 

Dry Flaky Skin

   Human skin normally produces a combination of oil and sweat.  These keep the skin soft and supple as seen in youth.  Dry, flaky skin occurs when the upper keratin layer of the epidermis dries out and becomes rough.  It can even become cracked.  If the skin loses water faster than the basal cells can replenish it, the keratin layer dries out, giving a rough appearance to the face. 

   Dry skin (xerosis) can start out with small, white scales that come and go.  It can progress to reddening and cracking of the skin.  Many sufferers complain that their face is tight to the point of cracking.  Dehydrated skin can become itchy, and further scratching can lead to the breakdown of the keratin layer of the skin with subsequent skin infections. 

   Dry, flaky skin with redness must be separated and distinguished from contact dermatitis, which is due to poison ivy or other plants, insects, or exposure to chemicals such as dyes, metal, earrings, rubber, drugs, or cosmetics.  Dry, flaky skin must also be separated from skin diseases such as eczema, seborrhea, psoriasis, ichthyosis, and some kidney, thyroid, and liver diseases. 

   There is a hereditary tendency to dry, flaky skin.  Blond, fair-skinned, thin-skinned teenagers may not have much trouble with the oiliness of the skin, but will have dry skin as early as their twenties.  Brunettes with thicker, oilier skin can suffer from flakiness of their facial skin.  In fact, all types of skin are susceptible to this problem. 

   A mild soap, which is fragrance-free, should be used twice daily.  Some choices include Eucerin, Neutrogena or Cepaphil.  top

Moisturizers

   Moisturizers absorb into the dry keratin layer of the epidermis, causing the dry flakes to pump out, giving the appearance of increased moisture.  All moisturizers include three similar ingredients: 

Occlusives:  They block the evaporation of water.

Humectants:  They attract water

Emollients:  They smooth the skin by filling in the spaces between the dry flakes and pumping up the dry keratin layer.

   The thickness of the moisturizing cream varies according to the oil-water ratio.  The thicker the product, the more oil it contains, which is important for very dry, sensitive skin.  These products work effectively and are inexpensive for people who have very dry skin, but do not have a long lasting therapeutic effect on the skin.

   Glycolic acid and vitamin C containing products are excellent for the skin. Applying the lotion twice daily changes the keratin layer of the epidermis, making it more compact, smoother, and gives the skin a brighter sheen.  The effectiveness of this lotion will depend on your type of skin, the type of soap you use, and the amount of humidity you have in your home.  Most skin types find the Glycolic acid lotion near perfect to maintain moist skin.  Depending on the dryness of your skin, it may be necessary to apply sparingly a moisturizer over the Glycolic lotion from time to time.  A facial buff-puff used gently is another way of keeping the dead keratin layer to a minimum.   top

Sunscreens

   There is no ideal sunscreen.  A sunscreen should have a broad spectrum, blocking out both UVA and UVB radiation.  It should be waterproof, non-irritating, non allergic, cosmetically elegant, and inexpensive.  Sunscreens are measured in SPF or Sun Protection Factor.  The number is derived from the minimal redness dose of protected skin over a minimal redness dose of unprotected skin.  They exclusively measure UVB, not UVA protection. A SPF of 8 blocks 87.5% of the UVB. A SPF of 15 blocks 93.3% of UVB.  A SPF of 29 blocks 96.6% of UVB.  So, as you go up from 15 in SPF, your efficiency in blocking the sunlight does increase proportionally.  All the experiments are done with a dose of sunscreen that is much thicker than is the usual application in practice.  Therefore, use a sunscreen with an SPF of 15 or greater.  As the SPF does not measure UVA protection, sunscreens should also contain an ingredient to block UVA.

   There are other factors that affect the amount of radiation that the skin receives.  Cloudy days do not block out ultra-violet radiation.  They may block out up to 15% depending on the thickness of the cloud.  Reflection of sand, water, and snow increase the amount of ultra-violet exposure that one can receive.  For every 1,000 feet above sea level, there is a significant increase in the amount of ultra-violet radiation exposure.  Most mountain climbers and skiers are aware of this.  Ultra-violet radiation is strongest during the day between 10 A.M. and 3 P.M. and it is advisable to avoid exposure during these hours.  It has been said that a 4% to 8% loss in the ozone layer could raise the risk of skin cancer by 15 %.

Sunscreen Ingredients

   Sunscreen ingredients vary in protection.  Some block only UVA or UVB radiation; some block both.

   Pure PABA blocks UVB only and stains the skin yellow.  Five percent of the population is allergic to it and the industry is phasing it out.  PABA esters block UVB and there is less staining, but 10 % of the population is allergic to this as well.

Sunscreens containing Zinc or Titanium dioxide are very effective in blocking UVA and UVB.