What does skin cell turnover mean?
Skin cell turnover usually refers to renewal of the epidermis, the outer layer of skin, rather than replacement of every layer underneath. Keratinocytes, the main surface skin cells, form in the basal layer at the bottom of the epidermis. Their daughter cells move upwards, mature and flatten. At the surface, the cells eventually loosen and fall off.1
Skin keeps renewing throughout life, rather than closing for a scheduled refit. Normal renewal maintains the tissue; repair responds to damage. These are connected processes, but they are not interchangeable.2
Why are there different turnover times?
Cell division, movement towards the surface and final shedding are different stages. A number describing one stage is not automatically the time needed for the whole process.1
| What the timing describes | Time |
|---|---|
| Normal renewal of keratinocytes | 15 to 30 days |
| Movement of daughter cells from the basal layer to form the surface layer | 28 to 60 days |
| Movement outwards within the outermost layer before shedding | About 14 days |
| A modelled estimate of total epidermal turnover on the inner forearm | 45 days |
The 45 day estimate uses surface shedding rates to calculate total epidermal turnover on the inner forearm. Treat it as a site specific estimate, not an exact countdown for your face or entire body. The practical answer is several weeks, with the timing depending on which part of renewal you mean.3
Is faster turnover always better?
No. Renewal speeds up when the epidermis is injured and in some skin diseases, particularly psoriasis. Faster turnover is therefore not, by itself, a sign of healthier skin.1
The epidermis is a protective barrier, not just the part of skin that gets photographed. It helps keep microbes out and prevents loss of internal fluids. Continuous renewal preserves that barrier's integrity as skin encounters its surroundings.4
Routine turnover also does not mean an injury will disappear after one renewal cycle. Adult skin wounds generally heal with scar formation, which is different from the ongoing replacement of epidermal cells.4
Where this answer comes from
- 1Principles of dermatological practice. Structure of the epidermisdermnetnz.org
- 2Immune-Epithelial Cross Talk in Regeneration and Repairpmc.ncbi.nlm.nih.gov
- 3Epidermal 'turnover time'--a new examinationpubmed.ncbi.nlm.nih.gov
- 4Embryonic skin development and repairpmc.ncbi.nlm.nih.gov
