The use of 感触+ に in this sentence: Direction or cause?


「これからもよろしく」

「上等だよ」

重ねられた左手の感触にそわそわ感を滲ませつつも、本日２回目の「上等だよ」をかまされた。

The character are holding hands (重ねられた左手) and the narrator complains this is
the second time he gets 「上等だよ」 today.

そわそわ感を滲ませつつも by itself (leaving つつも aside) it's akin to "an uneasy feeling is
made spread".

What I'm not quite sure is the use of 感触に.

Does it spread into the 感触に or does it spread because of 感触に?

I understand 感触に can be used for the cause of something for example (for
example あまりの寒さに目を覚ました) however I'm not sure if it's the case with 感触 here.

Does it spread into the touch or does it spread /because/ of the touch?




It's " _because of_ the sensation". This is に used to [mark the cause of a
psychological reaction](https://japanese.stackexchange.com/q/72042/5010). Also
note that this 滲む is not "to spread" but "(for an emotion) to show up":

> ### 滲む
>
> ❹内部にあった感情や気持ちが顔などの表面にあらわれる。にじみ出る。「苦悩の色［無念の思い］が顔ににじむ」「文面に愛情がにじんでいる」
>
> 出典: 大修館書店 明鏡国語辞典 第三版

So "重ねられた左手の感触にそわそわ感を滲ませつつも" means "While allowing restlessness to show up (on
his face) due to the sensation of the overlapped left hand..." or "With a look
of restlessness on his face due to the feeling of the overlapped left hand,
..."

