Grammar - Zero Conditional

The Zero Conditional

Usage
We use the zero conditional to talk about things which always happen if a particular action takes place. These can be scientific facts, or things we believe are always true.

When you take exercise, your heart beats faster.
If I drink milk, I get stomach ache.

If water reaches 100 degrees, it boils.
This conditional is used when the result will always happen. So, if water reaches 100 degrees, it always boils. It's a fact. I'm talking in general, not about one particular situation. The result of the 'if clause' is always the main clause.

If I eat peanuts, I am sick.
This is true only for me, maybe, not for everyone, but it's still true that I'm sick every time I eat peanuts.

If people eat too much, they get fat.
If you touch a fire, you get burned.
Snakes bite if they are scared

We can use if or when with the same meaning:
If you take exercise, your heart beats faster.
When I drink milk, I get stomach ache.

Zero conditional:

The zero conditional uses if/when + present simple, and present simple:

If/When you heat water to 100°C, it boils.

Positive

When she eats too much cake, she feels bad.
We always have a good time if we go dancing.

Negative

I feel upset when he doesn’t answer my calls.
If you mix white and yellow, you don’t get orange.

Question

What comes out of a volcano when it erupts?
Do eyelashes grow again if you cut them off? Yes, they do. / No, they don’t.

The zero conditional and time

We use the zero conditional to talk about things which are always true. We use the present tense, but we are talking about all time (past, present and future).

If you multiply 9 by 10, it makes 90.
Plants grow when they get water and sunshine.

Ref. BBC Learning English