[chris (OP)]

Question sent to me this week by Amber, who listens to our programme on the Gold Coast, Queensland...

If the body replaces itself every so often (I realise that different bits are replaced at different rates), then, when the skin replaces itself, why are scars, age spots etc not replaced as well, but are replicated?  (This would apply to, say, damaged muscle or other internal tissues?)

What do you all think?

[chris (OP)]

Scars form when the normal architecture of the skin tissue is lost, particularly the base-layer of the skin - the dermis - when the stem cells are located which replace the skin cells that drop off (every 28 days or so).

A full-thickness injury to a piece of skin disturbs the normal arrangement of skin cells and promotes the deposition of fibrous tissue to strengthen and repair the lesion. This also has the effect of changing the appearance of that patch of skin. These changes can include altered thickness, fibrosis, pigmentation (more, or less) and vascularity.

Scar do re-model over time, because skin is constantly replacing itself, but if the template that the replacement is following is itself different to "normal" skin, owing to a prior injury, then the turnover process merely replaces what is already there, leaving a persistent mark.

[vhfpmr]

I have a 48 year old scar on my arm and a 53 year old one on my knee, they used to be very conspicuous, but you have to look quite hard to find them now.

[chris (OP)]

I have a 48 year old scar on my arm and a 53 year old one on my knee, they used to be very conspicuous, but you have to look quite hard to find them now.

Indeed, scars do remodel, but the extent to which they disappear will depend upon the severity and scale of the original injury, the age at which that injury was inflicted (younger bodies tend to heal better than older ones) and where on the body the scar has formed (some anatomies heal better than others).

[MayoFlyFarmer]

I can say from my own research that we see an initial accumulation of senescent cells at the site of a healing wound/forming scar tissue, but these cells most definitely disappear over time (matter of weeks, at least in mice) indicating that the cells in that part of the tissue ARE being turned over, even if that structure of the scar remains.