Når jeg tygger, bløder jeg fra tandkødet, så jeg skyller munden.

Når means when. It introduces a time clause, so Når jeg tygger means when I chew.

In Danish, når is commonly used for:

• something that happens repeatedly or generally
• something expected in the future

So here it gives a general situation: whenever I chew, this happens.

This is because of normal Danish word order.

The first part, Når jeg tygger, is a subordinate clause. After a subordinate clause comes the main clause, and in a Danish main clause the finite verb usually comes in second position.

So:

• Når jeg tygger, bløder jeg fra tandkødet
• literally: When I chew, bleed I from the gums

This is a very important Danish pattern:

• Når jeg kommer, spiser vi
• If it rains, bliver jeg hjemme

If the main clause came first, it would be:

• Jeg bløder fra tandkødet, når jeg tygger

Tygger means chew or am chewing, depending on context.

Its infinitive (base form) is at tygge = to chew.

Here:

• jeg tygger = I chew / I am chewing

Danish present tense is often used where English might use either the simple present or the present continuous.

Danish does not usually make the same strong distinction that English does between:

• I chew
• I am chewing

The present tense jeg tygger can cover both ideas, and context tells you which one is meant.

In this sentence, because of når and the overall meaning, it sounds like a general repeated situation:

• When I chew, ...

So present tense is exactly what you would expect.

Bløder comes from at bløde, which means to bleed.

So:

• jeg bløder = I bleed / I am bleeding

In the sentence:

• bløder jeg fra tandkødet = I bleed from the gums

It is an intransitive verb here, meaning no direct object follows it.

Fra means from.

So:

• bløder fra tandkødet = bleed from the gum(s)

This is a natural way in Danish to indicate the source of the bleeding.

You could think of it as:

• the bleeding comes from the gum tissue

Tandkødet means the gums or more literally the gum tissue.

It is built from:

• tand = tooth
• kød = flesh
• tandkød = gum / gum tissue
• tandkødet = the gum / the gum tissue

Danish often forms nouns by combining smaller words into one compound word. English does this too sometimes, but Danish does it much more regularly.

So tandkød is a normal Danish compound noun.

Because tandkød is usually treated as a mass noun or collective noun, like gum tissue, rather than as separate countable pieces.

So Danish often uses:

• tandkødet = the gums / the gum tissue

Even though English often says the gums in the plural, Danish commonly uses the singular definite form here.

Here så means so.

It links the two parts:

• I bleed from the gums, so I rinse my mouth

It shows a consequence or result.

In other contexts, så can also mean:

• then
• so
• such

But in this sentence, so is the best match.

This is a very common Danish pattern with body parts.

Danish often uses the definite form instead of a possessive word like my, your, his, etc., when it is already obvious whose body part it is.

So:

• jeg skyller munden = literally I rinse the mouth
• but in natural English: I rinse my mouth

Other examples:

• jeg vasker hænderne = I wash my hands
• han børster tænderne = he brushes his teeth
• hun brækkede benet = she broke her leg

Using min mund is possible in some contexts, but it is less natural here.

• mund = mouth
• munden = the mouth

Danish often adds the definite article to the end of the noun instead of using a separate word like the.

So:

• en mund = a mouth
• munden = the mouth

That is why the sentence has munden.

There are commas because the sentence contains multiple clauses.

• Når jeg tygger is a subordinate clause
• bløder jeg fra tandkødet is a main clause
• så jeg skyller munden adds another clause/result

The first comma separates the when-clause from the main clause.

The second comma before så helps separate the result part. Comma usage in Danish can vary somewhat depending on comma style, but this punctuation is normal and understandable.

Yes, you could express a similar idea with derfor.

Compare:

• ..., så jeg skyller munden = ..., so I rinse my mouth
• ... Derfor skyller jeg munden = ... Therefore I rinse my mouth

Så is often more everyday and flowing in this kind of sentence. Derfor can sound a bit more explicit or formal.

Also note the word order with derfor:

• Derfor skyller jeg munden not
• Derfor jeg skyller munden

because skyller must stay in second position in the main clause.

Most likely it describes a repeated or general situation.

Because of:

• Når = when / whenever
• present tense verbs like tygger, bløder, skyller

the sentence sounds like:

• Whenever I chew, my gums bleed, so I rinse my mouth

If you wanted a more clearly one-time event, Danish would often use different wording or add more context.