Background <p>Asymmetric mydriasis, or unequal pupil size, requires careful evaluation to exclude serious neurological conditions. Pharmacologic causes are well-known, but reports have mainly involved prescription antiperspirants for underarm use. This case is novel because it describes, to our knowledge, the first instance of bilateral mydriasis and anisocoria caused by a non-prescription facial antiperspirant. This highlights a new public health concern related to easily accessible consumer products.</p> Case presentation <p>A young female presented with acute, unequally enlarged pupils (right pupil 7.5 mm, left pupil 4.5 mm), light sensitivity, and blurred near vision. Direct light reflex was absent in the right eye and sluggish constriction in the left eye, with no other ocular abnormalities detected on examination. The patient reported applying a facial antiperspirant patch (SWEATROL®) near her eyes the previous night. The patch contains glycopyrrolate, an anticholinergic agent. A diagnosis of pharmacologically-induced anisocoria and mydriasis was made. The patient was advised to stop using the product. All symptoms resolved completely within 48 h without any medical treatment.</p> Conclusion <p>This case demonstrates that potent anticholinergic agents in over-the-counter facial products can cause significant ocular side effects if used incorrectly. The easy availability of such products online, often without clear safety warnings, increases consumer risk. Eye care practitionersroutinely inquire about the use of topical cosmetic products in patients present ingwith unexplained asymmetric mydriasis. This case highlights the need for improved product labeling and enhanced public education to reduce the risk of similar iatrogenic events.</p>