Typically the skin does not absorb topical substances, but certain chemicals will allow absorption into the blood stream through the skin. This phenomenon is called transcutaneous absorption.
This is how the nicotine patches and Birth Control patches work.
This minimal answer was provided by A Massage Therapist's Guide to Pathology by Ruth Werner.
It can be applied directly to the hand. However, it is unlikely to have any effect due to absorption into the blood. Even with the microgram level dosages required to produce a psychotropic effect, transcutaneous (skin) absorption is expected to be minimal. If a person is warm, sweaty, etc., the dilated blood vessels near the skin combined with the sweat allowing for easier absorption may actually make absorption possible. However, ingestion is much more likely to be effective.
Transcutaneous electrical nerve stimulation
Yes
Yes
Yes
Yes
Yes
Yes
Application of surface , (transcutaneous) neuro-stimulator
Yes
Yes
Yes