te ga kayui toki wa, kono kuriimu o sukoshi tsukeru.

topic particle

Breakdown of te ga kayui toki wa, kono kuriimu o sukoshi tsukeru.

• を: direct object particle
• が: subject particle
• この: this

Questions & Answers about te ga kayui toki wa, kono kuriimu o sukoshi tsukeru.

Why is it 手がかゆい and not 手をかゆい?

Because かゆい is an i-adjective meaning itchy, and the body part that has that condition is often marked with が in Japanese.

So:

• 手がかゆい = My hand is itchy / The hand itches
• Literally, it is closer to As for the hand, it is itchy than to I itch the hand

Using を would not work here, because かゆい is not an action verb acting on hand. It describes a state or condition.

This pattern is very common with body parts and sensations:

• 頭が痛い = My head hurts
• のどが痛い = My throat hurts
• 目がかゆい = My eyes are itchy

What is the role of ときは in this sentence?

とき means when or at the time when.

So:

• 手がかゆいとき = when your hand is itchy
• 手がかゆいときは adds は, which marks that whole time expression as the topic: as for when your hand is itchy...

This gives the sentence a conditional/situational feel:

• 手がかゆいときは、このクリームを少しつける。 = When your hand is itchy, apply a little of this cream.

The は often adds a sense like:

• in that case
• in that situation
• as for those times

Why is there a は after とき?