Porth's Essentials of Pathophysiology, 4e

1151

Structure and Function of the Integumentum

C h a p t e r 4 5

skin, reducing transepidermal water loss, and restoring the lipid barrier’s ability to attract, hold, and redistrib- ute water. Moisturizing agents can be classified as emol- lients, humectants, and occlusives. Emollients are fatty acid–containing lotions that replenish the oils on the skin surface, but usually do not leave a residue on the skin. They have a short duration of action and need to be applied frequently. Humectants are the additives in lotions, such as α -hydroxy acids and urea, that draw out water from the deeper skin layers and hold it on the skin surface. However, the water that is drawn to the skin is transepidermal water, not atmospheric water; thus, continued evaporation from the skin can actually exac- erbate dryness. α -Hydroxy acids are derived from fruits, hence the abundance of fruit additives in over-the-coun- ter shampoos and lotions. Urea is a nitrogenous sub- stance that has been quite effective in reducing xerosis when combined with lotions. It is a humectant at lower concentrations (10%), but in higher concentrations (20% to 30%) it is mildly keratolytic. Clinical trials of urea have indicated its utility compared with ammo- nium lactate (lactic acid) lotion and glycerin. Occlusives are thick creams that contain petroleum or some other moisture-proof material. They prevent water loss from the skin. They are the most effective agents for relieving skin dryness, but because of their greasiness and lack of cosmetic appeal, some people do not wish to use them. Lotion or cream additives include corticosteroids or mild anesthetics, such as camphor, menthol, lidocaine, or benzocaine. These agents work by suppressing itch- ing while moisturizing the skin. Using room humidifi- ers and keeping room temperatures as low as possible to prevent water loss from the skin also may be help- ful. Soaps with moisturizers may be helpful. Glycerine soaps, although popular and visually appealing, are drying and can exacerbate the symptoms. Variations in Dark-Skinned People Some skin disorders common to people of African, Hispanic, or East Indian descent are not commonly found in those of European descent. Other skin disor- ders, such as skin cancers, affect light-skinned persons more commonly than dark-skinned persons. Because of these differences, serious skin disorders may be over- looked, and normal variations in darker skin may be mistaken for anomalies. As noted earlier, skin color is determined by the mela- nin produced by the melanocytes. Although the number of melanosomes in dark and white skin is the same, black skin produces more melanin, and more quickly, than white skin. Because of their skin color, dark-skinned persons are better protected against skin cancer, premature wrinkling, and aging of the skin that occurs with sun exposure. A condition common in people with dark skin is too much or too little color. Areas of the skin may darken after injury, such as a cut or scrape, or after disease con- ditions such as acne. These darkened areas may take many months or years to fade. Dry or “ashy” skin is also a common problem for people with dark skin. It often

Common Normal Variations in Dark Skin

TABLE 45-1

Variation

Appearance

Futcher (Voigt) line

Demarcation between darkly pigmented and lightly pigmented skin in upper arm; follows spinal nerve distribution; common in black and Japanese populations Line or band of hypopigmentation over the sternum, dark or faint, lessens with age; common in Latin American and black populations Linear dark bands down nails or diffuse nail pigmentation; brown, blue, or blue-black Blue to blue-gray pigmentation of oral mucosa; gingivae also affected Hyperpigmented creases, small hyperkeratotic papules, and tiny pits in creases Hyperpigmented macules; can be multiple with patchy distribution, irregular borders, and variance in color

Midline hypo-

pigmentation

Nail

pigmentation

Oral

pigmentation Palmar changes

Plantar changes

Developed from information in RosenT, Martin S. Atlas of Black Dermatology. Boston, MA: Little, Brown; 1981.

is uncomfortable, and it also is easily noticed because it gives the skin an ashen or grayish appearance. Although using a moisturizer may help relieve the discomfort, it may cause a worsening of acne in predisposed persons. Normal variations in skin structure and skin tones often make evaluation of dark skin difficult. The darker pigmen- tation can make skin pallor, cyanosis, and erythema more difficult to observe. Therefore, verbal histories must be relied on to assess skin changes. The verbal history should include the client’s description of her or his normal skin tones. Changes in skin color, in particular hypopigmenta- tion and hyperpigmentation, often accompany disorders of dark skin and are very important signs to observe when diagnosing skin conditions. Common variations in dark skin and nails are described in Table 45-1.

SUMMARY CONCEPTS

■■ Skin lesions are a loss of skin integrity and rashes are temporary skin eruptions.They are the most common manifestations of both skin and many systemic diseases.They vary in size and color; they can be flat (macule or patch), palpable (papule, plaque, or nodule), or fluid-filled elevations (vesicle or bullae). ■■ Erosions involve a loss of the superficial epidermis, and an ulcer a loss of the epidermis and papillary layer of dermis.

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