Gloves reduce your sense of touch, increasing the likelihood that you might accidentally tear a page, smear pigments, dislodge loose fragments — or worse, drop the book.
And whatever their associations with cleanliness, cotton gloves attract dirt. They also tend to make hands sweat, generating moisture that can damage a page. Rubber gloves, while moisture-proof and generally better fitted to the hand, are too grabby.
While there are some exceptions, librarians overwhelmingly agree the best way to handle a rare book is with clean hands and caution.
There are exceptions to the bare-hands rule. Books including some kinds of photographic materials are best handled with gloves (the Library of Congress recommends “clean nitrile gloves”). The same goes for books made from ivory or encased in metal bindings, or certain kinds of cloth.
And then there are poison books. In the 16th and 17th century, budget-minded bookbinders sometimes recycled cheap manuscript waste paper as a binding, coating it with arsenic-laced green paint to mimic leather. And in the Victorian period, some publishers used binding cloth dyed with colors like Scheele’s green, an industrially produced hue also containing arsenic. But, according to experts, so long as you don’t lick the book you will be fine.