What is the difference between 「おそれがある」 and 「かもしれない」?

In Japanese, there are many situations where you want to say that something “may happen” or “there is a possibility that something will happen.”

Two expressions that often appear in such situations are 「おそれがある」 and 「かもしれない」.

For example:

「このまま雨が続くと、川があふれるおそれがあります。」
If the rain continues like this, there is a risk that the river will overflow.

「今日は午後から雨が降るかもしれません。」
It may rain this afternoon.

Both expressions talk about something that has not happened yet.
However, they are not the same.

「かもしれない」 is a general expression used to show possibility.
On the other hand, 「おそれがある」 includes a stronger sense of warning that something bad may happen.

In other words, both expressions show possibility,
but 「おそれがある」 sounds more serious and carries a stronger sense of caution.

「かもしれない」 is a broad expression of possibility

「かもしれない」 is very commonly used in both daily conversation and writing.
It means “there is a possibility that...” or “it may be so.”

Example sentences

1. 「彼はもう駅に着いているかもしれません。」
   He may have already arrived at the station.

2. 「明日は忙しいかもしれないです。」
   I may be busy tomorrow.

3. 「この問題は、思ったより難しいかもしれません。」
   This problem may be more difficult than I expected.

4. 「あの人は日本人かもしれません。」
   That person may be Japanese.

The key feature of 「かもしれない」 is that it can be used very broadly.

It can be used for good things.
It can be used for bad things.
It can also be used for simple guesses.

For example:

「来月、給料が上がるかもしれません。」
My salary may go up next month.

「今日は電車が遅れるかもしれません。」
The train may be delayed today.

As you can see, 「かもしれない」 can be used regardless of whether the content is good or bad.

「おそれがある」 expresses caution about a bad result

「おそれがある」 does not simply mean that something is possible.
It means that there is a possibility that something undesirable may happen.

Example sentences

1. 「この薬は、強い眠気を引き起こすおそれがあります。」
   This medicine may cause strong drowsiness.

2. 「台風の影響で、交通が大きく乱れるおそれがあります。」
   Due to the typhoon, transportation may be severely disrupted.

3. 「このままでは、情報が外部に漏れるおそれがある。」
   If things continue like this, there is a risk that the information will leak outside.

4. 「大雪のため、停電のおそれがあります。」
   Because of heavy snow, there is a risk of a power outage.

The important point is that 「おそれがある」 is basically used with negative or undesirable content.

For example:

「試験に合格するおそれがある」

This is not normally said.
The meaning can be understood, but it sounds quite unnatural.

That is because 「おそれがある」 includes a feeling of worry, anxiety, or warning.

The most important difference: simple possibility or warning about a bad result

The difference between these two expressions can be summarized like this.

「かもしれない」
It simply says that something is possible.

「おそれがある」
It says that something bad may happen, and that caution is necessary.

Compare the following two sentences:

1. 「今日は雪が降るかもしれません。」
   It may snow today.

2. 「このまま気温が下がると、道路が凍結するおそれがあります。」
   If the temperature continues to fall, there is a risk that the roads will freeze.

Sentence 1 simply gives a weather prediction.
Sentence 2 warns the listener to be careful about a dangerous result.

This difference is very important.

「おそれがある」 is a formal expression

「かもしれない」 sounds natural in daily conversation.
In contrast, 「おそれがある」 is often used in news reports, warnings, explanations, business documents, and other formal writing.

Common situations

Weather and disaster warnings
Product warnings
Government or company announcements
Explanations of accidents or trouble
Medical and legal documents

For example, in the news, you may often hear:

「今夜遅くから明日にかけて、大雨となるおそれがあります。」
There is a risk of heavy rain from late tonight through tomorrow.

Even if you use 「かもしれません」 in this situation, the meaning can still be understood.
However, 「おそれがあります」 sounds more objective and more suitable for giving a warning.

「かもしれない」 is natural in conversation, while 「おそれがある」 is natural in explanations

For example, in a conversation with a friend:

「明日、試験の結果が出るかもしれないよ。」
The exam results may come out tomorrow.

This sounds natural.

However:

「明日、試験の結果が出るおそれがあるよ。」

This sounds unnatural.

On the other hand, in an announcement or news report:

「通信障害により、一部サービスが利用できなくなるおそれがあります。」
Due to a communication failure, some services may become unavailable.

This sounds natural.

If you say:

「利用できなくなるかもしれません。」

the meaning is not wrong, but it sounds a little lighter as a warning.

So, a useful way to think about the difference is:

For everyday guesses, use 「かもしれない」.
For formal warnings, use 「おそれがある」.

「おそれがある」 is closer to an objective warning than a personal feeling

「おそれがある」 is often used when the speaker is not simply making a casual personal guess.
It is often used to show a possible danger or disadvantage based on some objective reason.

For example:

「この橋は老朽化が進んでおり、倒壊のおそれがあります。」
This bridge is aging, and there is a risk that it may collapse.

In this sentence, the speaker is not just saying something casually.
It sounds as if there is some condition or evidence that supports the danger.

On the other hand:

「この橋、古そうだから壊れるかもしれないね。」
This bridge looks old, so it might break.

This is natural in conversation, but it sounds more personal and lighter.

Common mistakes made by learners

1. Using 「おそれがある」 for good things

For example:

「来年、売り上げが増えるおそれがあります。」

This usually sounds unnatural.
An increase in sales is normally a good thing.

A more natural sentence would be:

「来年、売り上げが増えるかもしれません。」
Sales may increase next year.

However, depending on the context, an increase in sales could lead to a bad result.
In such a special context, 「おそれがある」 may be possible.
Still, as a basic rule, it is safer to remember that 「おそれがある」 is used for bad results.

2. Using 「おそれがある」 too often in daily conversation

「彼、今日来ないおそれがある。」

The meaning is understandable, but it sounds too formal for ordinary conversation.

In normal conversation, this is more natural:

「彼、今日来ないかもしれない。」
He may not come today.

3. Not noticing the difference in weight between 「かもしれない」 and 「おそれがある」

「かもしれない」 can be used for light guesses.
「おそれがある」 sounds heavier and gives a stronger sense of warning.

For example:

「少し遅れるかもしれません。」
I may be a little late.

and

「重大な遅延のおそれがあります。」
There is a risk of a serious delay.

These two sentences create very different impressions.

They are similar, but often cannot be replaced freely

Look at the following sentence:

「この食品は、高温で保存すると品質が低下するおそれがあります。」
If this food is stored at high temperatures, there is a risk that its quality will decline.

This sounds natural.
It is a common style for a warning label.

If you change it to:

「品質が低下するかもしれません。」

the meaning is close, but the warning becomes weaker.

On the other hand:

「彼はまだ寝ているおそれがある。」

This sounds quite unnatural.

Here, it is just a simple guess, so the natural sentence is:

「彼はまだ寝ているかもしれない。」
He may still be sleeping.

In other words, although the meanings are sometimes close, the nuance and usage are quite different.

A simple way to understand the nuance

When you are not sure which one to use, think as follows.

「かもしれない」
Something may happen. It can be used for both good and bad things.

「おそれがある」
Something undesirable may happen. It includes caution or warning.

You can also think of it this way:

「かもしれない」 is suitable for conversational guesses.
「おそれがある」 is suitable for warnings in explanations and formal writing.

With these two points, the difference becomes much easier to understand.

Compare with example sentences

1. 「明日は雨が降るかもしれません。」
   It may rain tomorrow.

2. 「この地域では、今夜遅くに土砂災害のおそれがあります。」
   In this area, there is a risk of landslides late tonight.

Sentence 1 is a general prediction.
Sentence 2 warns about danger.

Let’s look at another pair.

1. 「彼はその話を知らないかもしれません。」
   He may not know about that story.

2. 「この情報をそのまま公開すると、個人情報が漏れるおそれがあります。」
   If this information is published as it is, there is a risk that personal information may leak.

Sentence 1 is a natural guess about a person.
Sentence 2 is a warning about a bad result.

Conclusion

「おそれがある」 and 「かもしれない」 both express possibility.
However, they differ greatly in weight and usage.

「かもしれない」 is a broad expression of possibility that is easy to use in daily conversation.
「おそれがある」 is a more formal expression that shows the possibility of a bad result and encourages caution.

Once you understand this difference, Japanese in news reports and warning notices becomes easier to read.
You will also be able to choose more natural expressions when writing or speaking.

If you want to learn subtle differences in Japanese through example sentences and practice questions, visit https://rapid-jt.com/ and check how these expressions are actually used.