Jennifer Lopez reportedly swears by Crème de la Mer, and judging by her amazingly smooth honey skin, we'd definitely use tubs of it if our wallets were kind enough to us. And when Jenny McCarthy said we shouldn't vaccinate our kids, oh my GOD let's listen to her because it makes kids autistic and we have no idea why, but we'll do it because Jenny McCarthy says so!

And the one day you're like "Ok, really?"

So why do we listen to celebrities? Why are celebrities used to endorse products? Aren't they as human as you are? Don't they know as much as you do?

Two researchers from Canada's McMaster University and the Harvard School of Public Health came up with a number of possible reasons. According to Steven Hoffman and Charlie Tan, some theories were drawn from economics, marketing, psychology, and sociology to explain why the average viewer - YOU - might buy into, say, Jenny McCarthy's anti-vaccine nonsense.

Published in the British Medical Journal's Christmas issue, they are:

Signals
Endorsements by celebrities act as markers that differentiate endorsed items from those of competitors.

Herd behaviour
Celebrities activate people’s natural tendency to make decisions based on how others have acted in similar situations.

Meaning transfer
People consume endorsed items to acquire the endorsing celebrities’ traits, which have become associated with the product.

Halo effect
The specific success of celebrities is generalised to all their traits, biasing people to view them as credible medical advisers.

Classical conditioning
The positive responses people have towards celebrities come to be independently generated by endorsed items.

Self conception
People follow advice from celebrities who match how they perceive (or want to perceive) themselves.

Cognitive dissonance
People unconsciously rationalise following celebrity medical advice to reduce the psychological discomfort that may otherwise result from holding incompatible views.

Social networks
Celebrity advice reaches the masses by spreading through systems of people linked through personal connections.

Social capital
People follow celebrity medical advice to gain social status and shape their social identities.