The present invention generally relates, in certain aspects, to systems and methods for application to the skin, and control of actuation, delivery, and/or perception thereof. For example, certain aspects of the invention are generally directed to devices for delivering to and/or withdrawing fluid or from subjects, e.g., to or from the skin and/or beneath the skin. In one aspect, the delivery and/or withdrawal of fluid is at least partially obscured. For example, the obscuration may be by time, and/or by sensory obscuration (e.g., by providing tactile, olfactory, auditory, and/or visual sensations). Certain aspects of the invention are generally directed to devices able to automatically deliver to and/or withdraw fluid from the skin and/or beneath the skin after activation, e.g., where the fluid is delivered and/or withdrawn without the need for any additional intervention. The devices may be activated by any suitable technique. In other aspects, a device may be contained in a package, and when removed from the package, the device may be constructed and arranged to be able to deliver and/or withdraw fluid when the device is applied to the skin, and in some cases, automatically and/or without any further intervention by the subject or another person.
