Skin layers and needle depth

Needle depth decides which skin layer is reached. Facial skin is under 1 mm thick on the eyelid and close to 2 mm on the nasal tip, so devices set depth area by area.

Methods and devices

Outside to inside

The layers of the skin

1. Stratum corneum

The dead outer layer. FDA guidance treats products that only disrupt this layer, for exfoliation or a smoother look, as generally not medical devices. Devices that reach the living epidermis and dermis are regulated.[1][2]

2. Epidermis

Microneedling passes through the epidermis without removing it. At 1 year after collagen induction therapy, biopsies showed a 40% thicker stratum spinosum with normal rete ridges.[1][2]

3. Papillary dermis

Fifteen passes of a 2 mm, 192-needle roller make about 250 holes per square cm reaching the papillary dermis, depending on pressure. New collagen formed at a depth of 5-600 micrometers with a 1.5 mm needle.[1]

4. Reticular dermis

The target of RF microneedling. Insulated needle electrodes create heated zones of denatured collagen in the reticular dermis while sparing hair follicles, glands and fat. New dermal tissue replaced these zones by 10 weeks.[1][2][3]

5. Depth settings by area

SkinPen guidance: forehead 0.25-1.0 mm, nose 0.25-0.75 mm, around the orbital rim 0.25-0.5 mm, facial acne scars up to 1.5 mm. Facial skin measured 0.57 mm on the upper eyelid and 1.91 mm on the nasal tip by ultrasound. Real penetration matched pen settings up to 1.0 mm and was less consistent at 1.5-2.5 mm.[1][2][3]

6. Nerves, vessels and fat

Nerves lie no shallower than about 2 mm, shallowest around the eye. Major facial arteries lie no shallower than 3-5 mm. RF microneedles reach 3.5 to 4 mm. The FDA has reports of fat loss and nerve damage after RF microneedling.[1][2][3]