Если зуд не проходит, лучше показать руку врачу.

This is a very common Russian pattern: лучше + infinitive.

It means something like:

• it’s better to...
• you’d better...
• one should probably...

Russian often leaves the subject unstated when the meaning is general or when you is understood from context. So лучше показать руку врачу literally feels like better to show the hand to a doctor, but in natural English it usually means you’d better show your hand to a doctor.

So the person is implied, not named.

In Russian, проходить / пройти can mean to pass, to go away, or to subside, especially for symptoms or unpleasant conditions.

So:

• зуд проходит = the itching goes away / subsides
• боль проходит = the pain goes away
• кашель проходит = the cough is going away

This is just the normal verb Russian uses for symptoms disappearing. English uses several different expressions, but Russian very often uses проходить in this sense.

Не проходит is present tense and is very natural in this kind of condition:

• Если зуд не проходит... = If the itching isn’t going away / doesn’t go away

Russian often uses the present tense here to describe an ongoing state or situation. It focuses on what is happening now and continuing.

If you said если зуд не пройдёт, that would sound more like:

• if the itching does not go away
• with a stronger sense of future result

Both can make sense in some contexts, but не проходит is very natural when talking about a symptom that is continuing at the moment.

This is about verbal aspect.

• показать = perfective
• показывать = imperfective

Here, показать is used because the sentence recommends a single completed action: showing the hand to a doctor.

So лучше показать руку врачу means:

• it would be better to show your hand to a doctor
  (one concrete action)

If you used показывать, it would sound more like a repeated, ongoing, or general process, which does not fit as well here.

Because руку is the accusative case, and it is the direct object of показать.

• nominative: рука = hand
• accusative: руку = hand as the thing being shown

So:

• показать руку = to show the hand

This is the normal pattern: the thing you show goes in the accusative.

Actually, врачу is correct here, and it is in the dative case because показать кому? что? means to show someone something.

So:

• показать руку врачу = to show the hand to the doctor

Here the doctor is the recipient of what is being shown, so Russian uses the dative without a preposition.

Compare:

• пойти к врачу = to go to the doctor
• показать руку врачу = to show the hand to the doctor

So к врачу is used with movement toward the doctor, but врачу is used with showing something to the doctor.

Not exactly.

• пойти к врачу = to go to the doctor
• показать руку врачу = to show your hand to a doctor

The second one is more specific. It implies not just visiting the doctor, but specifically having the doctor look at your hand.

In real life, the two ideas are closely connected, but grammatically and semantically they are not identical.

Because this is a condition, not a time statement.

• Если = if
• Когда = when

The sentence means: If the itching does not go away, it’s better to show your hand to a doctor.

That is conditional: the second action is recommended only under that condition.

If you used когда, it would sound more like when the itching doesn’t go away, which suggests the speaker treats it as a fact or expected event rather than a condition.

Here лучше means something like:

• it’s better
• you’d better
• it would be best

Russian often uses лучше + infinitive to give advice in a softer, less direct way than a command.

So:

• Лучше показать руку врачу
  = You’d better show your hand to a doctor

It is advice, not an order.

Yes. Russian can make the person more explicit:

• Если зуд не проходит, вам лучше показать руку врачу.
• Если зуд не проходит, тебе лучше показать руку врачу.

These mean:

• If the itching doesn’t go away, you’d better show your hand to a doctor.

But Russian often omits вам / тебе when it is clear from context. The shorter version sounds very natural.

Russian often omits possessive words like my, your, his, and so on when the meaning is obvious from context.

So показать руку врачу naturally means show your hand to a doctor here, even though your is not stated.

If needed, Russian could say:

• показать свою руку врачу

But that is usually unnecessary and can sound heavier than the simple version.

Yes. Russian word order is flexible, though different orders can change emphasis.

The given sentence:

• Если зуд не проходит, лучше показать руку врачу.

is very natural and neutral.

Other possible versions include:

• Если зуд не проходит, руку лучше показать врачу.
• Лучше показать руку врачу, если зуд не проходит.

These mean basically the same thing, but the emphasis shifts slightly. Russian often moves words around for focus, rhythm, or style more freely than English does.

Зуд is a masculine noun meaning itching or itch as a symptom.

For example:

• сильный зуд = severe itching
• кожный зуд = skin itching

In this sentence, зуд is the subject of не проходит:

• зуд не проходит = the itching doesn’t go away

So although English might sometimes say it still itches, Russian here uses a noun: the itching is not passing.