Skin Sciences: Structure, Conditions & Contraindications
About a quarter of the exam tests whether you understand the skin you are working on: how it is built, what it does, how it ages, how hair grows out of it, and, most importantly, when a condition in front of you belongs to a physician rather than to an esthetician. The exam repeatedly frames this as a judgment question, giving you a description of skin and asking whether you treat, modify, or refer. Learning the layers and the lesion vocabulary is what lets you describe skin accurately without ever crossing into diagnosis.
The Layers of the Skin
Skin has three main layers. The epidermis is the outermost and is where every esthetic service takes place. From deepest to most superficial its layers are the stratum basale, spinosum, granulosum, lucidum, and corneum; a useful anchor is that the basale sits against the dermis and the corneum faces the world. Cell division and melanin production happen in the stratum basale, while the stratum corneum is dead keratinized tissue that you cleanse and exfoliate. The stratum lucidum is a clear layer found only on the palms and soles. Below the epidermis sits the dermis, divided into the papillary and reticular layers, containing collagen and elastin, blood vessels, nerve endings, sebaceous and sudoriferous glands, and hair follicles. Beneath that lies the subcutaneous layer of adipose tissue that insulates, cushions, and gives the face its contour. Because superficial services affect only the epidermis, they improve texture and tone but cannot rebuild dermal structure, which is exactly why deep wrinkles are not an esthetic promise.
What Skin Does, and How It Renews
The skin protects against injury and microorganisms, provides sensation, regulates body temperature through blood flow and perspiration, excretes waste through sweat, secretes sebum, and absorbs a limited amount of what is applied to it. Sebum and perspiration form the acid mantle, a thin slightly acidic film with a pH around 4.5 to 5.5 that discourages microbial growth and slows water loss; this is why highly alkaline cleansers leave skin tight and reactive. Epidermal cells are produced in the basal layer and take roughly a month in a young adult to migrate to the surface and shed, a cycle that slows steadily with age. That slowdown is the main reason mature skin looks duller: more dead cells linger on the surface and light no longer reflects evenly. It is also why appropriate exfoliation improves the look of mature skin, and why over-exfoliation, which strips the barrier, backfires.
Fitzpatrick Types, Pigmentation, and Photodamage
The Fitzpatrick scale classifies skin by how it responds to ultraviolet light, from Type I, which always burns and never tans, through Type VI, which is deeply pigmented and rarely burns. It predicts more than sunburn: higher Fitzpatrick types have melanocytes that respond vigorously to inflammation, so aggressive exfoliation, heat, or trauma can produce post-inflammatory hyperpigmentation that is worse than the original concern. Protocols for higher types begin conservatively and progress slowly, always with daily broad-spectrum sun protection. Melasma is a hormonally influenced hyperpigmentation that appears as symmetrical patches on the cheeks, forehead, and upper lip and is aggravated by both UV and heat. UVA has a longer wavelength that reaches the dermis and drives photoaging and pigment change, while UVB is the shorter wavelength largely responsible for burning; both contribute to skin cancer risk, which is what 'broad spectrum' on a sunscreen label refers to. Intrinsic aging is the genetically programmed decline over time, while extrinsic aging comes from sun, smoking, and pollution and is the part a client can actually control.
Lesions, Disorders, and Knowing When to Refer
Primary lesions are those present when a condition first appears, including macules, papules, pustules, vesicles, wheals, and tubercles. Secondary lesions develop as the condition progresses or heals and include crusts, scales, fissures, excoriations, ulcers, and scars. Open comedones, or blackheads, are follicular contents exposed to air and oxidized dark; closed comedones are trapped beneath the surface and appear as small white bumps. Milia are keratin-filled cysts with no follicular opening, telangiectasia are dilated capillaries visible as red lines, and sebaceous hyperplasia is an enlargement of sebaceous glands. Mild acne is within scope, but deep painful nodules and cysts with scarring are a medical condition and must never be extracted. Rosacea, eczema with broken or weeping skin, active herpes simplex, and anything crusted, spreading, or suspiciously changing all call for referral. A mole with asymmetry, irregular borders, uneven color, larger diameter, or recent change is avoided entirely and the client is encouraged, without a diagnosis, to see a physician.
Hair Growth and Its Cycle
Hair grows from a follicle nourished by the dermal papilla, and it moves through three phases. Anagen is the active growth phase, when the hair is fully attached and richly supplied; catagen is a short transitional phase in which the follicle shrinks; and telogen is the resting phase, after which the hair sheds. Waxing produces its longest-lasting result when hair is removed during anagen, because the hair comes out with the fullest structure attached. Since follicles cycle independently, regrowth appears at staggered intervals rather than all at once, which is why clients see stubble sooner than expected after a first appointment and why repeat visits on a schedule give smoother results. Two terms are frequently confused: hirsutism is excessive terminal hair in a male distribution pattern on a woman, often hormonally driven, while hypertrichosis is excessive growth in areas that are not normally hair-bearing. All hair removal performed by an esthetician is temporary; permanent removal by electrolysis or laser falls under different licensing.
Last updated: July 2026