THINGS really got hot under the collar for Zachary Quinto in his role as Spock on the set of “Star Trek: Into Darkness.”

The actor put on a special protective heat suit to film a fiery volcano scene, but it failed to protect him from the scorching heat.

Now the 36-year-old star is sporting an angry red scar on the back of his neck.

As he prepared for the scene, Zachary remembers thinking, “This is going to be great!”

But it was no fun for him after a strip of his flesh was exposed to the heat and he couldn’t relay the problem to director J.J. Abrams because the microphone in his helmet was busted.

“My neck skin got caught in between  the helmet (and my shoulder),” recalled Zachary, who thrashed around in the red-hot simulated volcano while Abrams and the rest of the crew remained safely out of range of the heat.

“I didn’t know how serious it was,” continued Zachary. “I didn’t know what was happening.”

But once the shot was completed and Zachary took off his helmet, the crew noticed that a patch of skin on his neck was singed so badly it had puckered into a raised welt.

Abrams told him: “It looked like there was a caterpillar on your neck!”

Fortunately, the actor’s significant other, “Glee” star Jonathan Groff, was able to comfort him.

Zachary later had another source of comfort. The sci-fi adventure rocketed to No.1 at the box office in its first weekend, raking in a blistering $70.6 million.