Если у тебя на ладони царапина, её нужно промыть водой.

Russian often omits есть in the present tense when it is not necessary.

So:

• У тебя на ладони царапина = literally At you, on the palm, [there is] a scratch
• A more expanded version with есть is possible in some contexts, but it often sounds less natural here.

Russian commonly uses the structure:

• у + genitive + noun to mean someone has ...

So у тебя ... царапина means you have a scratch.

Also, Russian word order is flexible. Putting на ладони before царапина helps set the location first: on your palm.

This is a very common Russian possession structure.

Instead of using a verb like to have, Russian usually says something like at someone there is...

• у = at / by
• тебя = genitive form of ты

So:

• у тебя царапина = you have a scratch
• literally: at you [there is] a scratch

More examples:

• У меня машина. = I have a car.
• У него время есть. = He has time.

This is one of the first big differences English speakers notice in Russian.

Because ладонь means the palm / inner surface of the hand, and in Russian you normally say something is on that surface, not in it.

So:

• на ладони = on the palm

This is just the standard Russian preposition used with body surfaces.

Compare:

• на руке = on the hand / arm
• на лице = on the face
• на ноге = on the leg

Even though English might sometimes think of a scratch as being in the skin, Russian expresses the location here as on the palm.

Ладони here is prepositional singular.

The preposition на often takes:

• prepositional when talking about location
• accusative when talking about motion toward something

Here it is location, so we use the prepositional:

• ладонь → на ладони

Compare:

• царапина на ладони = a scratch on the palm
• положить монету на ладонь = to place a coin onto the palm

In the second example, на ладонь is accusative because there is motion toward the palm.

Её refers to царапина.

Since царапина is:

• singular
• feminine

the pronoun must also be singular feminine:

• царапина → её = it

In English, we say it for objects like scratch, but Russian uses grammatical gender, so the pronoun changes based on the noun’s gender.

Examples:

• шрам (masculine) → его
• царапина (feminine) → её
• пятно (neuter) → его

So её нужно промыть means it needs to be washed/rinsed.

Нужно + infinitive is a very common impersonal way to say it is necessary to... / one should... / needs to...

So:

• её нужно промыть водой = it needs to be rinsed with water
• literally: it is necessary to rinse it with water

This sounds neutral and instructional, which is very natural in advice, medical directions, and general recommendations.

Compare:

• Ты должен промыть её водой. = You must rinse it with water.

  • more direct
  • can sound more personal or stronger

• Её нужно промыть водой.

  • more general
  • more like advice or a standard instruction

This is about prefixes and aspect.

1. мыть

This is the basic verb to wash. By itself, it is usually imperfective.

2. промыть

This perfective verb means something like:

• to rinse
• to wash through
• to clean by washing thoroughly

For a scratch or wound, промыть is the natural medical-type verb: you wash it out / rinse it.

3. Why perfective?

After нужно, both imperfective and perfective can appear, but they mean slightly different things:

• нужно промывать = it is necessary to wash/rinse it repeatedly or as a process
• нужно промыть = it is necessary to do this one complete action

Here the sentence means a single necessary action, so промыть is the right choice.

Because the instrumental case is often used for the means or substance by which something is done.

So:

• промыть водой = rinse with water
• literally: rinse by means of water

This is a very common pattern in Russian:

• писать ручкой = write with a pen
• резать ножом = cut with a knife
• мыть водой = wash with water

The noun вода changes to instrumental singular:

• вода → водой

Yes. Водой and водою are both instrumental singular forms of вода.

• водой is the more common modern form
• водою is more literary or stylistic

In everyday speech and practical instructions, водой is the normal choice.

Because Если introduces a subordinate clause.

The structure is:

• Если у тебя на ладони царапина = If you have a scratch on your palm
• её нужно промыть водой = it should be rinsed with water

In Russian, subordinate clauses introduced by если are separated by a comma.

This is true whether the if clause comes first or second:

• Если у тебя на ладони царапина, её нужно промыть водой.
• Её нужно промыть водой, если у тебя на ладони царапина.

Yes, that would also be correct.

Russian word order is flexible, and both versions are natural:

• Если у тебя на ладони царапина, её нужно промыть водой.
• Если у тебя царапина на ладони, нужно промыть её водой.

The difference is mainly emphasis and flow.

In the original:

• на ладони comes earlier, so the location is highlighted first.

In the alternative:

• царапина на ладони stays together as a noun phrase, which may feel slightly more straightforward to a learner.

Also, both:

• её нужно промыть
• нужно промыть её

are possible. Russian often moves words around for emphasis, rhythm, or style.

No.

• рука = hand / arm
• ладонь = palm

So на ладони is specifically on the palm of the hand, not just somewhere on the hand in general.

That is why the sentence is more precise than на руке.

Yes, but scratch is the basic meaning.

Царапина usually means:

• a scratch on the skin
• a scrape mark
• a small scratch on a surface

So it can be used for both people and objects:

• У меня царапина на пальце. = I have a scratch on my finger.
• На машине царапина. = There is a scratch on the car.

In this sentence, because of промыть водой, it clearly means a scratch on the skin.

Grammatically, it says your because of у тебя.

So literally it is addressing one person informally:

• If you have a scratch on your palm, it should be rinsed with water.

But in context, Russian often uses ты in instructions in a general sense, especially in conversational advice. So it can function like general advice to anyone being addressed informally.

If you wanted a more formal version, you could say:

• Если у вас на ладони царапина, её нужно промыть водой.

That is the polite/plural version.