Skin Sciences and Analysis
Skin Sciences and Analysis
This domain tests whether you can read a face before you touch it: histology, barrier function, skin typing, and the observation skills that turn a consultation into a safe plan.
Structure and barrier
The epidermis is the outer layer, with the stratum corneum on top and melanocytes in the basal layer; the dermis holds collagen, elastin, capillaries, sebaceous and sweat glands, and follicles; subcutaneous fat cushions. The acid mantle sits near pH 4.5–5.5. Alkaline cleansers raise surface pH, swell the corneum, and increase water loss. Transepidermal water loss (TEWL) is the practical measure of barrier damage.
Type versus condition
Skin type is genetic and stable: normal, dry, oily, combination. A condition is temporary and treatable: dehydration, sensitization, hyperpigmentation, acne, aging. Dry skin lacks oil; dehydrated skin lacks water and can appear on an oily face. Confusing the two produces the classic error of applying a heavy cream to a dehydrated, acne-prone client.
Fitzpatrick and analysis tools
Fitzpatrick I–VI estimates UV response and guides wax temperature, peel selection, and laser candidacy. A magnification lamp and palpation reveal texture; a Wood's lamp fluoresces blue-white on normal skin, orange-yellow over oily areas, violet over dehydration, brown over hyperpigmentation, and coral-red with pityrosporum. Note lesions as primary (macule, papule, pustule, nodule, wheal) or secondary (scale, crust, excoriation, scar). Anything asymmetric, irregular in border, multi-colored, over 6 mm, or changing goes to a physician - the ABCDE rule.
Worked example
A client with Fitzpatrick V skin, an oily T-zone, tight cheeks, and visible flaking after a foaming cleanser asks for an aggressive scrub. Reasoning: flaking plus oiliness points to dehydration and barrier irritation, not retained dead cells. The plan is a non-foaming cleanser, a humectant such as glycerin or hyaluronic acid, a light emollient, no scrub, no acids this visit, and a reduced wax temperature if hair removal follows.
Traps that cost marks
Equating oily with hydrated. Using a Wood's lamp as a diagnosis rather than an observation. Treating a changing mole as a cosmetic blemish. Calling rosacea "acne" and exfoliating it. Forgetting that Fitzpatrick V–VI skin hyperpigments and scars readily after inflammation.