The last razor blade in a pack of five lasts up to five times longer than all the others, researchers have found.

Consumer tests of all the leading brand razors found that, no matter which order they are used in, it is always the fifth one that is still in use up to two months later.

The first four blades in a pack are typically changed in between three days and a week while the fifth may be on the point of rusting before it is finally disposed of.

But the ‘magic’ blade isn’t without its drawbacks, admit the researchers from Queen’s University, Belfast. Among its minus points are more cuts, worse razor burn and longer shaving times.

Overall, the research team is recommending that consumers throw away four of the blades as soon as the new packet is opened and start using the fifth blade immediately.

“It means less down-time for the razor and faster recycling of the discarded blades so there are efficiency and environmental benefits too.”

The team is now working on a project to establish why ‘empty’ toothpaste tubes can still produce enough toothpaste for up to eight further days of teeth cleaning if squeezed hard enough.