Из-за аллергии на пыльцу моя сестра иногда чихает в парке.

Из-за means because of and it requires the genitive case.

The dictionary form is аллергия.
In the genitive singular, it becomes аллергии.

So:

• аллергия = allergy
• из-за аллергии = because of an allergy / because of the allergy

This is a very common pattern:

• из-за дождя = because of the rain
• из-за болезни = because of illness
• из-за шума = because of the noise

Also, из-за often introduces a cause that is negative or inconvenient, so it fits well with allergy.

Because the noun after аллергия is often expressed with на + accusative in Russian:

• аллергия на пыльцу = an allergy to pollen
• аллергия на кошек = an allergy to cats
• аллергия на орехи = an allergy to nuts

The dictionary form is пыльца.
Here it changes to the accusative singular:

• пыльца → пыльцу

So на пыльцу literally means to pollen, but in natural English we say to pollen only as part of allergy to pollen.

Моя means my, and it has to agree with the noun it describes.

The noun сестра is:

• feminine
• singular
• nominative here, because it is the subject of the sentence

So the possessive adjective must match it:

• мой брат = my brother
• моя сестра = my sister
• моё окно = my window
• мои друзья = my friends

That is why the sentence uses моя сестра, not мой сестра.

Чихает is the 3rd person singular present tense form of the verb чихать (to sneeze).

Conjugation:

• я чихаю = I sneeze / I am sneezing
• ты чихаешь = you sneeze
• он / она чихает = he / she sneezes
• мы чихаем = we sneeze
• вы чихаете = you sneeze
• они чихают = they sneeze

Since the subject is моя сестра (my sister), Russian uses она-type agreement, so:

• моя сестра чихает

It can mean both, depending on context.

Russian present tense often covers both:

• she sneezes
• she is sneezing

In this sentence, because of иногда (sometimes), the meaning is clearly habitual or repeated:

• моя сестра иногда чихает = my sister sometimes sneezes

So here it is not about one sneeze happening right now, but about something that happens from time to time.

Because в can mean either:

• in / inside a place → with the prepositional case
• into a place → with the accusative case

Here the meaning is location, not movement:

• в парке = in the park

The noun changes like this:

• парк → в парке

Compare:

• Она чихает в парке. = She sneezes in the park.
• Она идёт в парк. = She is going to the park.

So:

• where? → в парке
• to where? → в парк

Yes, Russian word order is fairly flexible, and иногда can move.

The sentence:

• Из-за аллергии на пыльцу моя сестра иногда чихает в парке.

is completely natural.

But you could also say:

• Моя сестра иногда чихает в парке из-за аллергии на пыльцу.
• Иногда моя сестра чихает в парке из-за аллергии на пыльцу.
• В парке моя сестра иногда чихает из-за аллергии на пыльцу.

The basic meaning stays the same, but the focus changes slightly.

In the original sentence, starting with из-за аллергии на пыльцу gives the reason early emphasis.

Very often, yes. Из-за usually introduces a cause that is problematic, unwanted, or negative.

Examples:

• из-за дождя = because of the rain
• из-за пробок = because of traffic jams
• из-за болезни = because of illness

So из-за аллергии sounds very natural, because an allergy is a negative cause.

For more neutral reasons, Russian may use other expressions, such as из-за, от, по причине, or just a different sentence structure depending on the context. But in everyday speech, из-за is extremely common for negative causes.

A useful breakdown is:

• Из-за аллергии на пыльцу = because of an allergy to pollen
• моя сестра = my sister
• иногда = sometimes
• чихает = sneezes
• в парке = in the park

So the structure is basically:

Reason + Subject + Adverb + Verb + Place

Russian often allows this kind of order, especially when the speaker wants to present the cause first.

Yes. You could say:

• Из-за аллергии на пыльцу сестра иногда чихает в парке.

But that would usually mean the sister in some context, not necessarily my sister.

If you want to be clear that the person is my sister, then моя is needed.

Russian often omits things that are obvious from context, but if the relationship matters or has not been established yet, keeping моя is better.

Russian has no articles.

So nouns like сестра, аллергия, and парк do not have separate words for a/an or the. Context tells you whether the meaning is definite or indefinite.

For example:

• сестра can mean a sister or the sister
• парк can mean a park or the park

In this sentence, English chooses the most natural article based on context, but Russian simply does not mark that distinction.

A natural stress pattern is:

Из-за́ аллерги́и на пыльцу́ моя́ сестра́ иногда́ чиха́ет в па́рке.

A few useful stress points:

• из-за́
• аллерги́и
• пыльцу́
• моя́
• сестра́
• иногда́
• чиха́ет
• па́рке

One pronunciation note: из-за is written with a hyphen and pronounced as one unit meaning because of.

Yes, it can.

The sentence naturally suggests that the sneezing happens in the park, and the reason is the pollen allergy. Since parks often contain lots of pollen, the location and the cause fit together.

If you wanted to make the park more clearly the trigger environment, you could also restructure the sentence in other ways, but the original already sounds natural and clear. It suggests something like:

• because of her pollen allergy, my sister sometimes sneezes in the park

So в парке is not just random location information; it works well with пыльца.