haesbichi ganghamyeon seonkeurimeul ballaya haeyo.

It has two parts:

• 햇빛이 강하면 = if/when the sunlight is strong
• 선크림을 발라야 해요 = you have to apply sunscreen

So the pattern is:

• [condition] + [what you should/must do]

This is a very common Korean sentence structure.

이/가 marks the subject of the clause.

Here, 햇빛이 강하면 means if the sunlight is strong.
The thing that is strong is 햇빛, so it takes the subject marker 이.

• 햇빛 = sunlight
• 이 = subject marker
• 강하면 = if it is strong

So 햇빛이 means the sunlight as the subject.

강하면 comes from 강하다, which means to be strong/intense.

It is formed like this:

• 강하다 → stem 강하-
• 강하- + -면 → 강하면

-면 means if or when.

So 강하면 means:

• if it is strong
• when it is strong

In this sentence, it means the sunlight is intense/strong.

For English speakers, this is a very common point of confusion.

강하다 is usually translated like an adjective in English: to be strong.
But in Korean grammar, words like this behave a lot like verbs. They conjugate directly.

For example:

• 강하다 = to be strong
• 강해요 = it is strong
• 강하면 = if it is strong

So even though it feels adjective-like in English, in Korean it is often called a descriptive verb.

을/를 marks the object of the verb.

Here, the verb is 바르다 = to apply/spread on.
What are you applying? 선크림.

So:

• 선크림을 바르다 = to apply sunscreen

Because 선크림 ends in a consonant, it takes 을 rather than 를.

발라야 해요 expresses obligation or necessity.

It comes from this pattern:

• -아/어야 하다 = have to / must / should

So:

• 바르다 = to apply
• 발라야 하다 = have to apply
• 발라야 해요 = have to apply / should apply

In everyday speech, this can sound anywhere from should to need to to have to, depending on context.

This is because 바르다 is a 르-irregular verb.

When verbs ending in 르 are followed by -아/어, they often change like this:

• 바르다 → 발라
• not 바러
• and not 바르야

So:

• 바르다
• 발라요
• 발라야 해요

This same pattern appears in other verbs too, such as:

• 모르다 → 몰라요
• 고르다 → 골라요

So 발라야 해요 is the correct conjugation.

Korean often leaves out the subject when it is obvious from context.

In English, you might say:

• you have to apply sunscreen

In Korean, it is very natural to just say:

• 선크림을 발라야 해요

The hidden subject is usually understood as:

• you
• we
• people in general

In this sentence, it most naturally means you should apply sunscreen or one should apply sunscreen.

해요 is the polite informal style, often called the -요 form.

So 발라야 해요 is polite and natural for everyday conversation. It is appropriate in many situations, such as:

• speaking to someone you do not know well
• speaking politely to a friend or customer
• giving general advice

Compare:

• 발라야 해요 = polite everyday
• 발라야 합니다 = more formal
• 발라야 해 = casual, less polite

It can cover all of those, depending on context.

Literally, -아/어야 하다 is closer to have to or must, but in real-life Korean it is often softer than English must.

In this sentence, it often feels like:

• you should apply sunscreen
• you need to apply sunscreen
• you have to apply sunscreen

Because this is health advice, English should is often the most natural translation, even though the Korean grammar is stronger than a simple suggestion.

Yes. 선크림 is very common in everyday Korean.

It is a loanword from English-style sun cream, and Koreans use it naturally to mean sunscreen or sunblock.

You may also see more technical or formal terms like:

• 자외선 차단제 = UV blocker / sunscreen

But in ordinary conversation, 선크림 is extremely common and natural.

Yes. Korean often describes sunlight, wind, smells, flavor, and other sensations with 강하다, meaning strong/intense.

So 햇빛이 강하다 means:

• the sunlight is strong
• the sun is intense

This is a very natural Korean expression. In English, we might also say:

• the sun is strong
• the sunlight is intense
• the sun is harsh

So this wording is completely normal in Korean.