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Skin layers

Skin has two main layers: the epidermis on the surface and the dermis below it, joined at the dermal-epidermal junction. The dermis has a thin upper part, the papillary dermis, and a thicker lower part, the reticular dermis. Each laser setting reaches a set depth.

Lasers and light

Outside to inside

The layers of the skin

1. Epidermis

The surface layer. In biopsies from 71 volunteers, the stratum corneum measured 11 to 18 microns and the living epidermis 57 to 82 microns, depending on body site. An erbium laser removes about 2.5 microns per pulse for each J/cm2 above its 1.6 J/cm2 threshold. The ablative 2,940 nm beam of a hybrid laser reaches up to 110 microns.[1][2][3]

2. Dermal-epidermal junction

The basement membrane, a dense collagen network, joins the epidermis to the dermis along a wavy line. It holds the two layers together and houses epidermal stem cells. Three months after fractional laser treatment, biopsies showed a more undulating junction (rete ridges).[1][2]

3. Papillary dermis

The thin upper dermis, distinct under the microscope from the reticular dermis below. In a split-face study the CO2 laser injured skin down to the papillary dermis. Fractional 1,550 nm columns reached 300 microns.[1][2][3]

4. Reticular dermis

The thicker lower dermis. In the same split-face study, a phenol peel reached the reticular dermis. A fractional CO2 prototype ablated to 1 mm at 23.3 mJ, and the non-ablative 1,470 nm beam of a hybrid laser coagulates to 700 microns.[1][2][3]

5. Pigment cells (melanocytes)

Pigment granules (melanosomes) sit inside melanocytes. In the 1983 experiments, 351 nm pulses damaged melanosomes within melanocytes and 577 nm pulses damaged small blood vessels. Darkening after CO2 resurfacing was more common in darker skin types.[1][2]

6. Skin thickness by area

Thickness varies across the face. In cadaver biopsies from 15 facial sites, the upper eyelid was thinnest; the nasal tip was 3.3 times thicker and the brow 2.8 times.[1]