A persistent question for those of us who write young adult literature is, What are we not allowed to do or say when writing for teenagers?

I usually answer with an anecdote about a near-crisis at my publisher nine years ago, regarding a single use of the F-word in my second novel (the F-word remained). Now, I say, we are long past that worry. A writer can go as dark and violent as it gets (see “The Hunger Games”). Sex is more than fine (see all of B. T. Gottfred’s giddy, explicit novels). Graphic, instructive, erotic, romantic, disappointing: Bring it all on! Even better, current Y.A. novels now have many L.G.B.T.Q. protagonists (see Meredith Russo’s “If I Was Your Girl”), which was not the case even 10 years ago. Now, I say, the sky is the limit.

But reader, I lie.

Religion. Religion is the last taboo.

Yes, there exist Y.A. novels that contend with religion or spirituality in some way — not a lot, but some. Francisco X. Stork’s “Marcelo in the Real World” has one of the best conversations about sex and religion I’ve ever encountered. Marcelo is deeply curious about God, and regularly talks to a rabbi about his religious questions.

I think Alex Sanchez’s beautiful, smart “The God Box,” about a gay teenager who comes out at a high school in a conservative Christian community, should be required reading for young people (my college students agree). Deborah Heiligman’s “Intentions” focuses on sex abuse in a Jewish community, and Brendan Kiely’s moving “The Gospel of Winter” does the same in the Catholic tradition. And we’ve come a long way from 2007, when “Does My Head Look Big in This,” by Randa Abdel-Fattah, a wonderful book, introduced the rare Muslim teenage character to American readers.