Refers to the emotional strength needed to not be easily upset by criticism.

Emotional Resilience

It's used figuratively to talk about emotional, not physical, toughness.

Figurative Use

Having a thick skin doesn't mean the person is insensitive, rather they cope well with difficulties.

Describes animals' actual skin, often used to discuss natural defenses against elements.

In this context, it's not generally used to describe human skin, but that of certain animals.

It emphasizes the skin's role in protecting animals from environmental elements.