know what the risk is of something unpleasant happening to you?

Risk Bites has already covered the difference between "hazard" - the potential

of something to cause harm - and "risk" - the probability or chance of harm occuring.

What we need to know is how do you get from one to the other?

If you want to put a number on the risk of something bad happening,

dose-response is what you need.

But what is it, exactly?

Try this experiment:

Hold your right ear lobe very lightly between your right index finger and your thumb.

What do you feel?

Probably not a lot.

Now increase your hold slightly.

You probably feel an increase in pressure on your ear.

Now pinch hard -

do you feel the pain?

Congratulations, you have just experienced dose-response!

The "dose" is the amount of pressure you put on your ear lobe,

and the "response" is the pain you feel.

The greater the pressure, the greater the response.

Dose-response is simply the relationship between how much of something our body is

exposed to, and the way it responds to that something.

When it comes to chemicals, the "dose" is the amount of stuff that gets into a

particular part of the body where it can do harm. And the "response" is the harm

a given amount of stuff does.

This becomes pretty important when a small amount of something is safe or

even good for you, while a large amount might to kill you.

A German-Swiss dude called Paracelsus put his finger on it, metaphorically speaking,

in the sixteenth century

when he declared that "it's the dose that makes the poison."

And in saying so he became a father of modern toxicology.

Dose-response is what allows scientists to connect hazard to risk,

and to put a number on the probability of something bad happening.

And because of this it is incredibly powerful.

But as we'll see in future Risk Bites in this series, it can also

get rather complex.

We'll be looking more closely at dose- responsive how it helps shed light on

risk over the next few months, but until then, stay safe.