Если ты будешь смывать тушь слишком быстро, глаза могут покраснеть.

Because смывать is an imperfective verb. Imperfective verbs form the future with быть + infinitive:

• я буду смывать
• ты будешь смывать
• он/она будет смывать

This future often emphasizes the process or action in progress.

Here, будешь смывать тушь suggests while you are washing the mascara off / if you wash it off in too hurried a way.

A perfective alternative like смоешь would sound more like if you wash it off completely / in one completed act. The sentence chooses будешь смывать because the focus is on how the action is done, not just on the finished result.

They are an aspect pair:

• смывать = imperfective
• смыть = perfective

Very roughly:

• смывать focuses on the process, repeated action, or general activity
• смыть focuses on the completed result

So:

• смывать тушь = to be washing off mascara / to wash off mascara in general
• смыть тушь = to wash off the mascara completely

In your sentence, the speaker is talking about the action as it happens, especially with слишком быстро (too quickly), so the imperfective fits well.

Ты means you in the singular informal sense.

It is not always required, because Russian often drops subject pronouns when the verb ending already shows who is meant. So Russian speakers could also say:

• Если будешь смывать тушь слишком быстро, глаза могут покраснеть.

That still clearly means if you wash off mascara too quickly...

However, ты may be included:

• for clarity
• for emphasis
• because the sentence is addressing someone directly

So it is natural, but not strictly necessary.

Here тушь is in the accusative singular, because it is the direct object of смывать.

You are washing off what?
→ тушь

For this noun, the accusative singular looks the same as the nominative singular:

• nominative: тушь
• accusative: тушь

That is normal for many inanimate nouns.

Also, in this context, тушь usually means mascara.

Because Russian has no articles like a, an, or the.

So тушь can mean:

• mascara
• the mascara
• some mascara

The exact meaning depends on context.

In this sentence, English might naturally say your mascara or the mascara, but Russian usually does not need to say that unless it is important.

Russian often leaves out possessive words like my, your, his, etc. when they are obvious from context.

Since the sentence is talking about you removing mascara, it is already clear that it is your eyes. So:

• глаза могут покраснеть = your eyes may become red

Adding твои is possible, but it is usually unnecessary:

• твои глаза могут покраснеть

That would sound more explicit, and sometimes slightly more emphatic.

Because Russian naturally talks about eyes in the plural when referring to both eyes together.

• глаз = eye
• глаза = eyes

Since mascara removal affects the eye area generally, глаза is the normal choice.

Using the singular would change the meaning and suggest only one eye.

Могут покраснеть means may/can become red. It expresses a possible result, not a guaranteed one.

Compare:

• глаза краснеют = the eyes are getting red / tend to get red
• глаза могут покраснеть = the eyes may become red

So могут adds the idea of possibility.

This is very natural in warnings or advice, where the speaker means something like this could happen.

Because покраснеть focuses on the change of state: the eyes become red.

It is perfective because it presents that change as a single result:

• before: not red
• after: red

Compare:

• краснеть = to be reddening / to turn red / to blush (process or repeated behavior)
• покраснеть = to become red, to turn red once (result)

After могут, Russian often uses a perfective infinitive when talking about a possible one-time result:

• могут покраснеть = may become red

This is a very important difference between English and Russian.

In Russian, after если (if), a future form is completely normal when the condition refers to the future:

• Если ты будешь смывать...
• literally: If you will be washing...

English usually avoids will in this kind of if-clause, but Russian does not. So the Russian structure is correct and natural.

This is one of those places where you should not copy English grammar directly.

Слишком быстро means too quickly / too fast.

It modifies the verb phrase будешь смывать and tells you how the action is done.

So the warning is not about removing mascara in general, but about doing it over-hastily.

You can think of the structure like this:

• смывать = to wash off
• слишком быстро = too quickly

Together:

• смывать тушь слишком быстро = to wash off mascara too quickly

No, Russian word order is fairly flexible, although this version is very natural:

• Если ты будешь смывать тушь слишком быстро, глаза могут покраснеть.

This order is neutral and easy to understand:

1. condition first
2. result second

You could change the order for emphasis, for example:

• Глаза могут покраснеть, если ты будешь смывать тушь слишком быстро.

That still means the same thing, but now the result comes first.

Because the sentence has two clauses:

1. Если ты будешь смывать тушь слишком быстро
2. глаза могут покраснеть

In Russian, a subordinate clause introduced by если is normally separated by a comma.

So the comma here is required.

The word is written глаза, and in this form the stress is глазá.

So yes, the pronunciation matters:

• singular: глаз
• plural: глазá

For learners, stress is worth remembering because Russian stress is not always predictable.

In everyday modern usage, тушь very often means mascara, especially in contexts about makeup and eyes.

But historically and in other contexts, тушь can also mean ink or a dark liquid used for drawing or writing.

So context matters. In this sentence, because of смывать and глаза, it clearly means mascara.