Affect vs effect ?
English students and even native English speakers confuse these 2 words. This is often due to the similar spelling and pronunciation.
Let’s look at what these words mean and how to use them correctly.
affect
Pronunciation: /əˈfekt/
(to listen to the pronunciation, watch the video at the bottom of this post)
affect is usually a verb
“affect” is a verb 99% of the time. Conclusion: this is the only use of “affect” that you need to know.
(A verb defines an action, a state or an occurrence.)
Meaning:
“to affect” means “to influence” or “to make a difference to”
Examples:
Pollution affects the environment.
The cold weather is affecting my health.
The increase in the price of oil is affecting the economy.
Affect can also sometimes be used as a noun
This is extremely rare! You will probably never see or hear this use. I have included it for completeness.
Meaning:
“affect” is used in psychology to describe an emotion or mental state.
Example:
The patient had a happy affect.
effect
Pronunciation: /ɪˈfekt/
(to listen to the pronunciation, watch the video at the bottom of this post)
“effect” is usually a noun
(A noun defines a thing, person or place.)
Meaning:
“effect” means “result” or “consequence” or “influence”
We say that something has an effect ON something else.
Examples:
Smoking has an effect on health.
The noise had an effect on my concentration.
What are the effects of pollution on the environment?
“effect” can sometimes be a verb
This is a very formal and academic use. It’s not very common in everyday English. I have included it for completeness.
Meaning:
to produce a result.
to cause something to happen.
to accomplish / do.
Example:
The Prime Minister has effected many changes to the economy.
(This is just another way of saying “The Prime Minister has made many changes to the economy.”
2 ways to say the same thing
We can use “affect” as a verb OR “effect” as a noun to say the same thing:
Smoking affects health. 
Smoking has an effect on health.
The above 2 sentences are both grammatically correct and they mean the same thing.
It’s important not to mix the 2:
Smoking effects health. 
Smoking has an affect on health.
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