Even your smallest finger is not able to penetrate the ear canal far enough to contact the eardrum to cause any damage. If you stuck something smaller in diameter, then you could damage the eardrum, although most people develop discomfort before penetrating that far.

For the vast majority of adults, it is physically impossible for a finger to reach the eardrum. The human ear canal is roughly 2.5 to 3 centimeters (about 1 inch) long and is shaped like a slightly curved "S" tube. The eardrum (tympanic membrane) is located at the very end of this narrow canal, protected by a bend that prevents straight-line access. While your finger might be able to enter the first part of the canal, it is too wide to penetrate deep enough to touch the delicate membrane. However, this does not mean it is safe to stick your finger in your ear; doing so can push earwax deeper against the drum, causing impaction, or scratch the very thin, sensitive skin of the canal, leading to painful infections like "swimmer's ear." You also risk introducing bacteria or fungi into a dark, warm environment where they thrive. The medical golden rule is "never put anything smaller than your elbow in your ear," as even a fingernail can cause micro-tears that lead to significant discomfort, hearing muffledness, or even a ruptured eardrum if an object is used.