huyu ha neru mae ni kuriimu wo nuru you ni site imasu.

冬は uses は to set winter as the topic: as for winter or in winter.

So the sentence has a nuance like:

• As for winter, I make a point of applying cream before bed.

Using は can also imply a mild contrast, such as:

• In winter I do this
• maybe in other seasons I do not, or not as much

If you said 冬に, that would simply mark winter as a time when something happens, but 冬は sounds more natural here because the speaker is talking about a seasonal habit.

Japanese often leaves out the subject when it is obvious from context.

In this sentence, しています strongly suggests the speaker is talking about their own habit, so I is understood naturally. A full version could be:

• 私は冬は寝る前にクリームをぬるようにしています。

But this sounds more explicit than necessary. In normal Japanese, dropping 私は is very common.

寝る前に means before going to bed or before sleeping.

It breaks down like this:

• 寝る = to sleep / to go to bed
• 前 = before
• に = marks the time point

So literally it is:

• at the time before sleeping

This is a very common pattern:

• 食べる前に = before eating
• 出かける前に = before going out
• 寝る前に = before sleeping

Before 前, Japanese normally uses the dictionary form of the verb:

• 寝る前 = before sleeping
• 食べる前 = before eating
• 行く前 = before going

That is because the action in the verb has not happened yet relative to before.

By contrast, with 後 (after), you often use the past form:

• 寝た後 = after sleeping
• 食べた後 = after eating

So:

• 寝る前 = before you sleep
• 寝た後 = after you slept

The に marks the time when the main action happens.

So in:

• 寝る前にクリームをぬる

the cream-applying happens at the time before sleeping.

In many time expressions, に marks a specific point or occasion:

• 3時に = at 3 o’clock
• 出発の前に = before departure
• 寝る前に = before sleeping

Sometimes English speakers want to translate に every time, but it is better to think of it as a grammatical marker rather than a word with one fixed English equivalent.

The pattern is:

• dictionary form + ようにする
• ない-form + ようにする

This means to try to do, to make a habit of doing, or to make sure to do something.

So:

• クリームをぬるようにする
  = to make a point of applying cream
  = to try to apply cream regularly

The verb before ようにする is not there as the main finished action. It is part of a set expression.

Examples:

• 毎日運動するようにしています。
  = I try to exercise every day.
• 夜はコーヒーを飲まないようにしています。
  = I try not to drink coffee at night.

ようにしています means something like:

• I make a point of ...
• I try to ...
• I make it a habit to ...
• I make sure to ...

So the sentence does not just mean that the speaker is applying cream one time. It describes an ongoing personal habit or effort.

Compare:

• クリームをぬります。
  = I apply cream. / I will apply cream.
• クリームをぬるようにしています。
  = I make a point of applying cream.

The second version has the nuance of conscious effort or routine.

ようにしています is usually used when talking about an ongoing habit or continued effort.

So:

• ぬるようにしています
  = I am keeping up the habit of applying it
  = I try to do that regularly

If you said ぬるようにします, it would sound more like:

• I will try to apply it
• I’ll make it a habit to apply it

That sounds more like a decision from now on, rather than a current habit already in place.

So in this sentence, しています is natural because the speaker is describing what they generally do these days in winter.

Yes, ぬる（塗る） basically means to spread/apply something onto a surface.

That can include:

• paint
• cream
• ointment
• sunscreen
• lipstick
• glue

So with クリーム, ぬる is very natural:

• クリームをぬる = apply cream

English uses different verbs depending on context, but Japanese often uses ぬる broadly for putting a substance onto a surface.

Yes, you often can, but the nuance is a little different.

• ぬる（塗る） focuses on spreading something on a surface
• つける is more general: put on, attach, apply

With cream, both can work, but:

• クリームをぬる sounds very natural when you mean spreading it over the skin
• クリームをつける is also possible, but slightly less specific

So in this sentence, ぬる is a very good choice.

を marks the direct object of the verb.

Here:

• クリーム = the thing being applied
• を = object marker
• ぬる = apply/spread

So:

• クリームをぬる = apply cream

This is standard verb-object structure in Japanese.

Yes, the nuance is different.

• 冬は寝る前にクリームをぬっています。
  = In winter, I apply cream before bed.
  This states a habit fairly directly.

• 冬は寝る前にクリームをぬるようにしています。
  = In winter, I make a point of applying cream before bed.
  This adds the feeling of conscious effort, intention, or self-care routine.

So the original sentence sounds a little more like the speaker is being careful or disciplined about it.

A helpful breakdown is:

• 冬は = as for winter / in winter
• 寝る前に = before going to bed
• クリームを = cream + object marker
• ぬる = apply
• ようにしています = make it a habit / try to do

So the structure is basically:

• [time/topic] + [time before an action] + [object] + [verb] + ようにしています

You can think of it as:

• As for winter, before bed, I make a point of applying cream.

That is a very natural Japanese way to express a seasonal routine.