DENVER — The warning sign was just outside the theater door.

“Please be advised,” it cautioned, in capital letters. “This production contains: Strobe lighting effects. Sudden loud noises. Theatrical fog/haze. Scenes of violence. Adult language. Sexual situations. Adult humor and content.”

The subject was a play called “Vietgone,” about a Vietnamese couple who meet in a refugee camp in Arkansas during the Vietnam War. The Denver Center Theater Company was proud to present the boisterous comedy, but it was taking few chances about surprising audiences: Online, patrons who hovered over an alert on the theater’s website could get pop-up details on the timing of the show’s explosions.

Not so long ago, a theatergoer was handed a program, shown to a seat and left to enjoy the show. Then came notices about strobe lights and smoking. But now, following a trend bubbling up from college campuses, theaters across the country are offering increasingly comprehensive and specific trigger warnings.

The phenomenon has led to searching discussions at theaters large and small, pitting a traditional impulse — to preserve art’s ability to surprise, shock and stir — against a modern desire to accommodate sensitivities and not alienate paying customers.