Why can itching be contagious?

Thursday 7th March 2013
Submitted by Susan Blackmore
Mark Purcell, Ireland

Like yawning and coughing, scratching can be infectious. You see someone else scratching and soon you feel itchy yourself.

‘Itch transmission’ has been investigated by showing people pictures of fleas or ants. This can make them scratch, but watching someone else scratching produces the strongest response. A possible clue as to why this happens may be revealed when a drop of histamine is dropped on someone’s skin. This makes them itchy, but they scratch all over, not just where the drop was placed. This suggests a mechanism that makes us hypersensitive to skin sensations and lowers the threshold for wanting to scratch, which may be the cause of infectious scratching.

Why do we have it? Other primates behave this way too. One theory is that it evolved in social species to help them notice and deal with parasitic infestations.

Has a child ever been conceived in space?
previous qanda Article
Could the human mind ever run out of memory?
next qanda Article
Q&A Tabs

Phlegm is the mucous secretion of the respiratory passages. The cilia cells that line these passages are continually driving the phlegm upward to the throat, where it triggers the swallow reflex...

It depends on the temperature of the water. In cold water, the bacterial action that causes a body to bloat with gas may be so slowed that the body stays on the seabed. The skin will absorb water...

Gamma-ray bursts (GRBs) are extremely energetic flashes of radiation caused by the collapse of massive stars to form neutron stars or black holes. They are the most energetic events in the...

Beard hair is quite different to head hair; it is coarser, curlier and doesn't fall out as we get older. Comparatively little work has been done on the genetics of human hair colour, but it is...

You might think it would just be a question of learning to live without honey, but bees play an incredibly important role in agriculture as pollinators. Cereal crops are wind-pollinated but...

All female mammals have a clitoris, the sole purpose of which is to react to sexual stimulation, and presumably this stimulation has evolved to be pleasurable for most species. But establishing...

To create a sound, we have to set matter - whether it's a gas like air, a liquid or even a solid material - in regular motion, creating a wave of specific frequencies, which we hear as a sound of...

Mirrors don’t reverse left and right either – that’s just our interpretation of what happens. Your reflection in the mirror is actually reversed front to back – if you have...

Discovered by an American student named Gary Flandro in the mid-1960s, the slingshot manoeuvre usually involves spacecraft briefly 'coat-tailing' a planet orbiting the Sun, extracting some of the...

The ice disappears because the wind blows away water molecules that have evaporated or 'sublimed' from the ice, so the ice slowly shrinks in size. The molecules that escape are those with the...