Albert Barnes Commentary Job 4:15

"Then a spirit passed before my face; The hair of my flesh stood up." — Job 4:15 (ASV)

Then a spirit passed before my face – He does not suggest whether it was the spirit of a man or an angel who appeared in this way. The belief in such apparitions was common in the early ages and, indeed, has prevailed at all times. No one can demonstrate that God could not communicate his will in such a manner as this, or by a messenger sent from his immediate presence to impart valuable truth to people.

The hair of my flesh stood up – This is an effect that is often produced by fear. Sometimes the hair is made to turn white almost in an instant as an effect of sudden alarm, but usually, the effect is to make it stand on end. Seneca uses language remarkably similar to this in describing the effect of fear in Hercules Oetaeus:

Vagus per artus errat excussos tremor;
Erectus horret crinis. Impulsis adhuc
stat terror animis et cor attonitum salit,
Pavidumque trepidis palpitat venis jecur.

So Virgil:

Steteruntque comae, et vox faucibus haesit.

Aeneid ii.774.

See also Aeneid iii.48, iv.289. So also Aeneid xii.868:

Arrectaeque horrore comae.

A similar description of the effect of fear is given in the Ghost’s speech to Hamlet:

“But that I am forbidden
To tell the secrets of my prison-house,
I could a tale unfold whose lightest word
Would harrow up your soul, freeze your young blood,
Make your two eyes, like stars, start from their spheres,
Your knotty and combined locks to part,
And each particular hair to stand on end
Like quills upon the fretful porcupine.”

The fact referred to here – that fear or fright causes the hair to stand on end – is too well established and too common to admit a doubt. The cause may be that sudden fear has the effect of driving the blood to the heart (as the seat of vitality), leaving the extremities cold. The skin then contracts, and the effect is to raise the hair.