August 2017 DERMfoot
Faculty & Expert Opinion
M. Joel Morse, DPM
Step Up To The Scale
How many times a day to you see any of these: Stasis eczema, Eczema, Atopic Dermatitis, Contact dermatitis, Xerosis, Psoriasis, Lichen Planus. To some podiatrists the skin is just a structure you have to get past in order to get to the bones. But the skin problems are what brings patients into your office with symptoms like: tightness, tingling, itchiness, burning, scaling, flaking and lichenification. Don’t look past the skin for other podiatric concerns. The skin can be a “mirror” of what is going on in the body. Now as podiatrists we have less real estate than dermatologists but the lower legs and heel are notoriously problematic with dry skin symptoms. Just because we do not treat the hands, and forearms we still need to evaluate those areas so we get the big picture. The feet do not exist in a vacuum.
The skin acts as a barrier and protects underlying tissues from infection, desiccation, chemicals, and mechanical stress. Disruption of this function results in increased trans epidermal water loss (TEWL) and deceases in the stratum corneum water content (SCWC) and is associated with conditions like atopic dermatitis, eczema, xerosis, contact dermatitis and other chronic skin diseases. Moisturizers have been shown to improve these conditions through restoration of the integrity of the stratum corneum, acting as a barrier to water loss and replacement of skin lipids and other compounds (1) Despite the knowledge of well recognized aggravating factors, its etiology is an enigma, and the management of the condition is often suboptimal (2).
Anatomy of Dry Skin
In the foot and ankle region we have three types of skin: plantar skin which has no oil glands and the largest number of sweat glands anywhere, dorsal skin which is normal skin, and the skin overlying the shin which is thinnest and more prone to injury. Dry skin occurs when the skin’s outer layer (the stratum corneum) is depleted of water. The skin’s outer layer consists of dead, flattened cells that gradually move toward the skin’s surface and slough off. The cells of the stratum corneum have lost their nucleus and are rich in keratin and are known as “corneocytes” (3) Intercellular lipids bind the corneocytes together. When this layer is well-moistened, it minimizes water loss through the skin and helps keep out irritants, allergens, and germs. However, when the stratum corneum dries out, it loses its protective function. This allows greater water loss, leaving your skin vulnerable to environmental factors.
Under normal conditions, Skin requires a water content of 10-15% to remain supple and intact (4). This water gives the skin its soft, smooth, and flexible texture. The water comes from the atmosphere, the underlying layers of skin, and sweat. Oil produced by skin glands and fatty substances produced by skin cells act as natural moisturizers, allowing the stratum corneum to seal in water. The skin contains natural moisturizers: ceramides, glycerol, urea, lactic acid. These help rehydrate skin to prevent water loss. So that is the reason that many of the products out on the market contain urea, lactic acid, salicyclic acid, and glycol. They are trying to “mirror” the skin. The essential ingredient of an emollient is lipid (fats, waxes, and oils).
Ceramides are the natural moisturizing factors and are the major lipid constituent of the intercellular spaces of the stratum corneum. These lipids are thought to provide the barrier property of the epidermis (5). The link between skin disorders and changes in barrier lipid composition, especially in ceramides, is difficult to prove because of the many variables involved. However, most skin disorders that have a diminished barrier function present a decrease in total ceramide content with some differences in the ceramide pattern. Patients with skin diseases such as atopic dermatitis, psoriasis, contact dermatitis, and some genetic disorders have diminished skin barrier function (6).
We continuously lose water from the skin’s surface by evaporation. Under normal conditions, the rate of loss is slow, and the water is adequately replaced. Characteristic signs and symptoms of dry skin occur when the water loss exceeds the water replacement, and the stratum corneum’s water content falls below 10%. Any factor that damages the stratum corneum can interfere with its barrier function and lead to dry skin. The feet by and large are not subject to the typical factors which affect skin elsewhere including long hot showers and cold, dry air, detergents and solvents. The feet are more subject to chafing and rubbing due to walking as well as the interplay between socks and shoes.
Skin Structure and Ethnicity
A recent study has demonstrated that skin properties at the level of the stratum corneum vary considerably among ethnic groups. East Asian and Caucasian skin was characterized by low maturation and relatively weak skin barrier. African American skin was characterized by low ceramide levels and high protein cohesion in the uppermost layers of the stratum corneum. These data can be interpreted in terms of the high prevalence of xerosis in black skin and increased skin sensitivity in East Asian skin.
Transepidermal water loss is more in black skin than in Caucasian skin – predisposing to more xerosis. Ceramides are the major lipid constituent of lamellar sheets present in the intercellular spaces of the stratum corneum. These lamellar sheets are thought to provide the barrier property of the epidermis (7).
Ceramide levels in black skin is lowest – followed by whites, Hispanics, and Asian’s have the highest levels (8). So one can infer that blck skin is more prone to xerosis and the pathology due to xerosis.
In the African American communities “ashy” skin is used to describe dry skin. The skin is dry, cracked, and powdery – one can see the skin flakes more easily on dark skin. In our society the “ashy’ color is considered unacceptable – and many blacks use oils or petrolatum to make the skin shiny. (9)
Treatment of Dry Skin
The first step to treat dry skin is to add water to the skin and apply a hydrophobic (water hating) substance to keep it there.. The substances include water in oil creams and lotions or 100 % oil ointments to lock in the water. No matter what the cause of dry skin is – there are three topicals which are regularly used to treat the conditions. Occlusive mositurizers, Humectant emollients, and Keratylictyics. Emollient is the scientific name for moisturizer. For the most part Emollients work by retaining water in the skin where it is needed, as well as enabling the repair of damaged cells on the skin's surface. Emollients reduce water loss and prevent the skin from drying out. They also act as a barrier to the environment, preventing irritants penetrating the outer layer of the skin (epidermis) by creating a protective lipid film(10) such as petrolatum – prevent water loss only by acting as a layer of oil on the surface of the skin to trap water and prevent evaporation.
Humectant emollients
such as Eucerin – penetrate the stratum corneum and draws water from the dermis to retain it in the epidermis.
Keratolytics
– lactic acid, salicyclic acid, Glycolic acid – help remove scales. Many times all three are together in one product to get the three effects in one.
While topical steroids do not treat dry skin they do decrease the inflammation of the skin and the “itch” factor which is tied in with dry skin. Maximum hydration can be achieved with 60% propylene glycol in water applied (11) under occlusion. Topical steroid: mid potency for dorsal foot skin and on legs, and high potency to super high on plantar skin. All topicals have increased absorption thru the incomplete skin barrier.
When discussing choice of emollients a continuum exist between oily ointments and water based creams and lotions. Ointments are best for the driest of skin conditions and for use at home when one is not wearing tight clothes, or working with others. Application of ointments can cause folliculitis in hairy areas – an unusual issue in the foot and ankle. Frequent use of emollients reduce the need to steroids (12). To avoid or treat xerosis moisturize your feet right after a bath or shower and avoid soaking your feet in hot water for long time periods, using drying soaps on your feet or scrubbing your feet dry. Anecdotal and limited data suggest that gabapentin, cutaneous field stimulation, serotonin antagonists, and ultraviolet B phototherapy may attenuate itch in some of these patients.
References
1.Nolan, K Marmur, E Moisturizers: Reality and the skin benefits. Dermatologic Therapy. 25(3):229-233, May/June 2012.
2.Coderch L, López O, de la Maza A, Parra JL. Ceramides and skin function. Am J Clin Dermatol. 2003;4(2):107-29.
3.Watkins P .Using Emollients to restore and maintain Skin Integrity. Nursing Standard 22. 41. 51-57. May 6, 2008
4.Pons-Guiraud, A Dry skin in dermatology: a complex physiopathology.
Journal of the European Academy of Dermatology & Venereology. 21 Supplement 2:1-4, September 2007
5.Coderch L, López O, de la Maza A, Parra JL. Ceramides and skin function.
Am J Clin Dermatol. 2003;4(2):107-29.
6.Choi MJ, Maibach HI Role of ceramides in barrier function of healthy and diseased skin. Am J Clin Dermatol. 2005;6(4):215-23.
7.McKinley-Grant L. VisualDx: Essential Dermatology in Pigmented Skin. Lippincott. 2011. Pp 322
8.Aziz N. Xerosis and Eczema Craquele in McKinley-Grant L. VisualDx: Essential Dermatology in Pigmented Skin. Lippincott. 2011. Pp 316
9.Watkins P .Using Emollients to restore and maintain Skin Integrity. Nursing Standard 22. 41. 51-57. May 6, 2008
10.Scott S. Atopic dermatitis and dry skin. In: Krinsky D. Berardi R, Ferreri S, et al, eds. Handbook of Nonprescription Drugs. 17th ed. Washington, DC: American Pharmacists Association; 2012
11.Domino, F 5-Minute Clinical Consult 2014
12.
www.scientificamerican.com/article.cfm?id=how-does-sunscreen-protec
