Si eres alérgica, es mejor que no te rasques la picadura, aunque te moleste mucho.

Because alérgica agrees with the person being spoken to, and here the sentence is addressed to a woman.

• Si eres alérgica = If you’re allergic (speaking to a woman)
• If you were speaking to a man, it would be Si eres alérgico.

This is a very common feature in Spanish: many adjectives change ending to match gender.

Spanish usually uses ser for more permanent or defining characteristics, and estar for temporary states or conditions.

So:

• eres alérgica = you are allergic
  This treats being allergic as a characteristic of the person.

Using estar alérgica would sound unusual here.

In Spanish, after si meaning if, you normally use the present indicative when talking about a real or possible condition in the present or future.

So:

• Si eres alérgica... = If you’re allergic...

Spanish does not normally use the future after si in this kind of sentence.

Compare:

• Si vienes, te ayudo. = If you come, I’ll help you.
• Not Si vendrás...

This is a very important pattern to remember.

Because es mejor que... is a structure that usually triggers the subjunctive in the following clause.

So:

• es mejor que no te rasques = it’s better that you don’t scratch yourself / don’t scratch the bite

Here, rasques is the present subjunctive form of rascarse for tú.

This is common with expressions like:

• es mejor que...
• es importante que...
• es posible que...
• conviene que...

Because the verb is rascarse, and for tú in the present subjunctive, the form is te rasques.

Breakdown:

• infinitive: rascarse
• present indicative: te rascas
• present subjunctive: te rasques

The spelling change from c to qu happens to keep the hard k sound before e:

• rasco
• rasques

This is a spelling rule, not a pronunciation change.

Because rascarse is a reflexive verb here: to scratch oneself.

So:

• rascar = to scratch something
• rascarse = to scratch oneself

In this sentence, te means yourself:

• no te rasques la picadura = literally don’t scratch yourself the bite
• more naturally: don’t scratch the bite

Spanish often uses a reflexive structure where English just uses a normal verb.

La picadura means the bite or the sting, depending on context.

It can refer to:

• an insect bite
• a sting
• sometimes another kind of small skin bite/mark

In this sentence, it most likely means the insect bite/sting area.

Spanish often uses the definite article (el, la, los, las) with body parts or things closely connected to the body, especially when a reflexive pronoun already shows whose it is.

So instead of saying:

• scratch your bite

Spanish naturally says:

• rascarse la picadura

Similarly:

• Me duele la cabeza = My head hurts
• literally: The head hurts me

This is very normal Spanish structure.

Because aunque can take either the indicative or the subjunctive, depending on the meaning.

Here, aunque te moleste mucho uses the subjunctive because it means something like:

• even if it bothers you a lot
• even though it may bother you a lot

The speaker is not presenting the annoyance as a firm, stated fact; it’s more concessive and general.

If you said aunque te molesta mucho, that would sound more like:

• although it bothers you a lot
  with the annoyance treated as a known fact.

Both can be possible in the right context, but moleste fits this kind of advice very well.

Here te is not reflexive. It is the indirect object pronoun meaning to you.

So:

• molestar = to bother
• te moleste = it bothers you / it may bother you

Compare the two te pronouns in the sentence:

• no te rasques → reflexive (yourself)
• te moleste → indirect object (to you / you)

Same word, different grammatical role.

Because mucho is modifying the verb molestar, not an adjective or adverb.

• te moleste mucho = it bothers you a lot

Use muy before adjectives or adverbs:

• muy grande = very big
• muy lentamente = very slowly

Use mucho with verbs:

• me gusta mucho
• trabaja mucho
• me molesta mucho

It works like advice, and grammatically it looks like the same form used for a negative tú command:

• No te rasques = Don’t scratch yourself

In this sentence, though, it is inside es mejor que..., so it is part of a subordinate clause rather than a standalone command.

Still, the form is the same subjunctive form you see in negative tú commands.

Compare:

• No te rasques. = Don’t scratch.
• Es mejor que no te rasques. = It’s better that you don’t scratch.

Yes, that is possible, but it is slightly less direct and more general.

Compare:

• Es mejor que no te rasques la picadura.
  = directly addressing you

• Es mejor no rascarse la picadura.
  = It’s better not to scratch the bite in a more general way

Both are correct, but the original sentence sounds more personal because the speaker is advising a specific person.

Yes. You can tell from the verb forms and pronouns:

• eres
• te rasques
• te moleste

All of these match tú.

If the sentence were addressed to usted, it would be:

• Si es alérgica, es mejor que no se rasque la picadura, aunque le moleste mucho.

That would sound more formal.

It has three main parts:

1. Si eres alérgica
   = If you’re allergic

2. es mejor que no te rasques la picadura
   = it’s better that you don’t scratch the bite

3. aunque te moleste mucho
   = even if / although it bothers you a lot

So the pattern is:

• condition
  • main advice
    • concession

This kind of sentence structure is very common in Spanish.