Saya sapu krim pada ruam kecil di lengan saya.

In Malay, adjectives usually come after the noun they describe.

So:

• ruam kecil = small rash
• literally: rash small

This is normal Malay word order. A few more examples:

• rumah besar = big house
• kereta baru = new car
• buku lama = old book

They do slightly different jobs here:

• pada ruam kecil = on/to the small rash
  This shows the target of the action: where the cream is being applied.
• di lengan saya = on my arm
  This shows the location of the rash.

So the structure is roughly:

• I apply cream to the rash
• the rash is on my arm

In many contexts, di and pada can feel similar in English translation, but here pada fits the idea of applying something onto a target, while di marks a physical place.

The two saya words have different roles:

• the first Saya = I
• the last saya = my

Malay possession usually works by putting the possessor after the noun:

• lengan saya = my arm
• literally: arm my

So the repetition is completely normal.

Yes. Sapu means to spread, to smear, or to apply by rubbing/spreading.

In this sentence, sapu krim means something like:

• apply cream
• rub cream on

It is a natural verb for things like cream, ointment, oil, or paint.

For example:

• Saya sapu ubat pada luka. = I apply medicine to the wound.
• Dia sapu mentega pada roti. = He/She spreads butter on the bread.

Good question. In formal standard Malay, you will often see the verb with the meN- prefix:

• Saya menyapu krim pada ruam kecil di lengan saya.

That is more fully marked grammatically.

But in everyday spoken Malay, it is very common to use the base verb after a subject pronoun:

• Saya sapu krim...

So:

• saya sapu = common, natural in speech
• saya menyapu = more formal or more standard written style

Both can be understood, but the version without the prefix is very common in conversation.

Here it means on my arm.

Even though di is often translated as in, it really means at / in / on, depending on context.

So:

• di lengan saya = on my arm
• di meja = on the table
• di rumah = at home / in the house

Malay di is broader than any single English preposition.

Malay does not normally use articles like a, an, or the.

So:

• krim can mean cream, the cream, or some cream
• ruam kecil can mean a small rash or the small rash

The exact meaning usually comes from context.

If needed, Malay can add words to be more specific, but very often it simply leaves articles out.

Yes, in the right context, especially in conversation or instructions.

• Sapu krim pada ruam kecil di lengan saya.

This could sound like:

• a note
• a diary-style sentence
• an instruction-like expression
• informal speech where the subject is understood

But if you want a full neutral sentence meaning I apply cream..., including Saya is clearer.

A simple breakdown is:

• Saya = I
• sapu = apply/spread
• krim = cream
• pada ruam kecil = onto the small rash
• di lengan saya = on my arm

So the sentence structure is basically:

Subject + Verb + Object + Target/Location

Malay word order here is quite similar to English, except for things like:

• adjectives coming after nouns
• possessors coming after nouns

Yes, depending on context.

Literally, ruam kecil is small rash. But in natural English, that might be translated as:

• a small rash
• a minor rash
• a slight rash

Malay often uses a straightforward adjective like kecil, while English may choose a more natural expression depending on the situation.

Yes, it is understandable and natural, especially in everyday use.

A few possible versions are:

• Saya sapu krim pada ruam kecil di lengan saya.
• Saya menyapu krim pada ruam kecil di lengan saya.
• Saya sapukan krim pada ruam kecil di lengan saya.

These are all related, but with slightly different style or grammar choices.

For a learner, the original sentence is a good, useful pattern for talking about applying something to a part of the body.