It is the veins that lie outside the muscle, not the deep veins, that become varicose. There are two theories about how varicose veins form and perhaps both are true.
The old theory says that the basic cause is failure of the valve at the connection with the deep vein in the muscle. Over time, the superficial vein will swell to cope with the extra blood, lose its elasticity and become a lumpy, blue, varicose vein. The swelling means that the next valve below will eventually be unable to close because its edges will no longer meet each other in the closed position. So, there is a domino effect, with each damaged valve eventually producing damage to the one below it. As it does so, more of the vein will swell and become varicose. This would happen very slowly over years.

Another theory, gaining ground among experts, says that the vein wall is inherently weak in people who get varicose veins. The vein swells and so the valves do not work properly.

First published on: embarrassingproblems.com
Reviewed and edited by: Fiona Elliott
Last updated: January 2021