Burnumun içi kuruyunca kaşıntı başlıyor.

It is a possessive noun phrase meaning the inside of my nose.

It breaks down like this:

• burun = nose
• burnum = my nose
• burnumun = of my nose
• içi = its inside / the inside

So:

• burnumun içi = the inside of my nose

This is a very common Turkish pattern:

• X-in Y-si = the Y of X

For example:

• evin kapısı = the door of the house
• arabanın rengi = the color of the car
• burnumun içi = the inside of my nose

Notice that both parts are marked:

• the first noun gets the genitive ending
• the second noun gets a possessive ending

Because in Turkish, when inside belongs to something, it usually takes a possessive ending.

So:

• iç = inside, interior
• içi = its inside / the inside of it

Since we are saying the inside of my nose, Turkish uses:

• burnumun içi

not just burnumun iç

This is the normal structure in Turkish. English often uses of, but Turkish marks this relationship with suffixes.

This happens because of a common sound change called vowel drop.

The dictionary form is:

• burun = nose

When certain suffixes are added, the middle vowel can drop:

• burun → burnum = my nose
• burnum → burnumun = of my nose

So the form looks shorter than you might expect.

This happens with some other body-part words too. For example:

• ağız → ağzım = my mouth
• boyun → boynum = my neck

So burnumun is completely regular.

Kuruyunca means when it gets dry, when it dries, or once it dries out, depending on context.

It comes from the verb kurumak / kuruyup kuruma- family, meaning to dry or to become dry. In this sentence the form is built with the suffix:

• -ınca / -ince / -unca / -ünce = when / once / after

So:

• kuruyunca = when it dries / when it gets dry

The y is a buffer consonant, added because the verb base ends in a vowel.

This suffix creates a time clause:

• Burnumun içi kuruyunca... = When the inside of my nose gets dry...

Its basic meaning is when or once.

In this sentence, kuruyunca most naturally means:

• when it gets dry
• once it dries out

Depending on context, English might sometimes translate this kind of form more loosely as if or even something close to because, but the core idea is a time relationship:

• first: the inside of the nose gets dry
• then: itching starts

So for this sentence, when is the safest understanding.

Because Turkish is expressing the idea as itching starts.

• kaşıntı = itch, itching, itchiness
• başlıyor = starts, is starting

So literally:

• kaşıntı başlıyor = itching starts

This is very natural Turkish.

A different way to express a similar idea would be with the verb kaşınmak:

• Burnumun içi kuruyunca kaşınmaya başlıyor.
• When the inside of my nose gets dry, it starts itching.

But the original sentence uses the noun kaşıntı and says itching begins.

They are different:

• burnumun içi is the subject of kuruyunca
• kaşıntı is the subject of başlıyor

So the logic is:

• The inside of my nose gets dry
• Itching starts

That is why the sentence does not mean that my nose starts drying or that the inside starts itching directly. The sentence is structured as:

1. burnumun içi kuruyunca = when the inside of my nose gets dry
2. kaşıntı başlıyor = itching starts

Because Turkish often leaves out pronouns when they are already clear from the suffix.

Compare:

• benim burnumun içi = the inside of my nose
• burnumun içi = the inside of my nose

Both are correct, but burnumun içi is more natural unless you want emphasis.

Turkish usually avoids unnecessary pronouns. The -um and -un endings already show the possession clearly.

Because burnumun içi and burnumun içinde mean different things.

• burnumun içi = the inside of my nose

  • this is a noun phrase
  • it can be the subject of a verb

• burnumun içinde = inside my nose / in my nose

  • this is a location phrase
  • it means in the inside of my nose

In this sentence, the thing that becomes dry is the inside of my nose, so Turkish uses:

• burnumun içi kuruyunca

If you said burnumun içinde, that would mean inside my nose as a location, which would not fit as well here.

Yes, and Turkish often uses the present progressive for things that happen regularly, naturally, or in a repeated real-life pattern.

• başlıyor literally looks like is starting
• but in context it can mean starts

So the sentence can express a general tendency:

• When the inside of my nose gets dry, itching starts.

Turkish -yor is not limited to actions happening right this second. It can also describe:

• current situations
• habits in context
• repeated experiences
• general patterns that feel vivid or real

So başlıyor is perfectly natural here.

The sentence follows a very common Turkish pattern:

• [subordinate clause] + [main clause]

Here:

• Burnumun içi kuruyunca = when the inside of my nose gets dry
• kaşıntı başlıyor = itching starts

So Turkish puts the when-clause first, and then the main statement.

A very literal order would be:

• Inside-of-my-nose when-getting-dry, itching starts

This kind of structure is extremely common in Turkish, especially with suffixes like -ınca.

Yes, it is natural and understandable.

It sounds like something someone might say when describing a physical symptom.

A few close alternatives are also possible, depending on style:

• Burnumun içi kuruyunca kaşıntı oluyor.
  = When the inside of my nose gets dry, itching happens.

• Burnumun içi kuruyunca kaşınmaya başlıyor.
  = When the inside of my nose gets dry, it starts itching.

But the original sentence is perfectly normal:

• Burnumun içi kuruyunca kaşıntı başlıyor.