Meine Nase ist zu, weil ich erkältet bin.

Because Nase is a feminine noun: die Nase.

The possessive word mein changes its ending to match the noun, so:

• mein for masculine/neuter in some forms
• meine for feminine singular here

So:

• mein Mund = my mouth
• mein Ohr = my ear
• meine Nase = my nose

In this sentence, meine Nase is the subject, so it is in the nominative case.

In German, all nouns are capitalized, not just proper names.

So:

• Nase = nose
• Erkältung = cold
• Haus = house

This is a standard rule in German spelling.

Here zu means something like blocked, closed up, or shut.

So Meine Nase ist zu is a common everyday way to say that your nose is stuffy or blocked.

Literally, it sounds like My nose is closed, but the natural English meaning is more like My nose is blocked/stuffed up.

A more explicit alternative is:

• Meine Nase ist verstopft. = My nose is blocked/stuffy.

No.

German zu has several different uses. In this sentence, it is not the infinitive marker.

Compare:

• Ich versuche zu schlafen.
  Here zu is the infinitive marker: to sleep

• Die Tür ist zu.
  Here zu means shut/closed

Your sentence uses the second meaning:

• Meine Nase ist zu. = My nose is blocked/closed up

Because weil is a subordinating conjunction.

In German, when a clause begins with a subordinating conjunction like weil (because), the conjugated verb usually goes to the end of the clause.

So:

• Ich bin erkältet. = I have a cold.
• ..., weil ich erkältet bin. = ... because I have a cold.

That is why you get:

• Meine Nase ist zu, weil ich erkältet bin.

and not:

• weil ich bin erkältet

Erkältet means having a cold or suffering from a cold.

So:

• Ich bin erkältet. = I have a cold.

It is used with sein in a very natural way in German.

Related words:

• die Erkältung = a cold
• sich erkälten = to catch a cold

So you may also see:

• Ich habe eine Erkältung. = I have a cold.

Both are natural, but Ich bin erkältet is especially common in everyday speech.

Yes, absolutely.

These are both natural:

• ..., weil ich erkältet bin.
• ..., weil ich eine Erkältung habe.

The difference is mostly about structure:

• ich bin erkältet uses an adjective
• ich habe eine Erkältung uses a noun

Both mean essentially the same thing in this context.

Because in German, a subordinate clause introduced by words like weil, dass, wenn, or obwohl is normally separated by a comma.

So this comma is required:

• Meine Nase ist zu, weil ich erkältet bin.

This is a very important punctuation rule in German.

Sometimes yes, but meine Nase is clearer and more natural on its own.

German often uses the definite article with body parts in certain constructions, for example:

• Die Nase tut mir weh. = My nose hurts.

But in a simple sentence like this, Meine Nase ist zu is very normal because it clearly tells you whose nose is blocked.

If you just say Die Nase ist zu, it can sound more general or depend more on context.

Yes, it is natural and idiomatic.

A German speaker would understand it immediately. It sounds like normal everyday speech.

Some common alternatives are:

• Meine Nase ist verstopft, weil ich erkältet bin.
• Ich bin erkältet, deshalb ist meine Nase zu.
• Ich habe eine verstopfte Nase.

All of these are natural, but Meine Nase ist zu is especially common in spoken, informal German.

The sentence has two parts:

1. Meine Nase ist zu
   This is the main clause.

   • Meine Nase = subject
   • ist = verb
   • zu = complement

2. weil ich erkältet bin
   This is the subordinate clause.

   • weil = because
   • ich = subject
   • erkältet = complement
   • bin = verb at the end

So the overall pattern is:

• main clause + comma + weil-clause

That is a very common German sentence pattern.