Caffeine patch

Caffeine can cross the blood-brain barrier, which means it can enter the brain and affect the nervous system directly. Caffeine is particularly good at blocking the A2A Adenosine receptor. Blocking the A2A receptor is thought to be responsible for promoting wakefulness.

Caffeine also affects other systems in the body such as heart rate, breathing rate, and blood vessels. It can also cause the release of neurotransmitters like monoamines and acetylcholine, which contribute to its stimulating effects.

Apart from blocking adenosine receptors, caffeine also blocks the inositol trisphosphate receptor 1, the ionotropic glycine receptor, and activates ryanodine receptors. Together these actions contribute to the stimulating effects of caffeine felt after consuming it.

Caffeine blocks an enzyme called phosphodiesterase, which leads to an intracellular increase in a molecule called cyclic AMP (cAMP). This increase activates another enzyme called protein kinase A, which can reduce inflammation. Caffeine also has an effect on another chemical called acetylcholine, by slowing down the activity of an enzyme that breaks it down in the body, cholinesterase thus leading to an increase in acetylcholine levels.[6]

Several studies measured the total amount of caffeine penetrated via patch on different anatomical sites and were ranked as follows:

1. Forehead
2. Arm
3. Post auricular region (behind the ear)
4. Abdomen.[8]

Researchers studied how skin aging affects the absorption of caffeine by the body. They found that older subjects absorbed more caffeine than younger subjects due to reduced sebaceous gland activity and skin lipid content. However, changes in skin hydration and corneocyte size could also play a role.[9]

A 2010 study showed that caffeine residue loosely sits on the skin and is not quickly absorbed. People who wash the skin around their caffeine patch showed significantly lower levels of caffeine. Therefore for maximum effects it is suggested to avoid washing the area where the patch is placed.[10]

Several studies have looked at the effect hair has on skin absorption. It has been demonstrated that hair follicles are considered a weak spot in the protective barrier against certain types of drugs. This suggests that increasing the number of hair follicles allows for a faster delivery of topically applied solutions.[11][12]

Caffeine is a first line treatment for neonatal apnea due to its metabolites' (theophyllines) effects on the lungs and breathing rate. Oral administration of medication in neonates is difficult for several reasons. Poor swallowing and GI compromise often lead to unpredictable and erratic dosing. This makes transdermal delivery of medications an ideal and promising choice. Studies have shown that caffeine applied twice daily in gel formulation in neonates is sufficient to maintain therapeutic levels of caffeine while avoiding oral dosing complications.[13][14]

Cellulite is a complex skin disorder involving multiple factors such as microcirculatory, lymphatic drainage, extracellular matrix, and excess fat accumulation. Caffeine has been hypothesized to help with this as it stimulates lipolysis (fat metabolism) and lymphatic drainage thus helping remove accumulated fat and toxins. Caffeine also increases blood flow through the microcirculation further assisting in removing toxins and waste products. Studies using caffeine patches at various concentrations show promising results in the treatment of cellulite.[6]

Caffeine has also been shown to reduce swelling around the eyes although this use is usually via a gel formula of caffeine.

Caffeine exerts antioxidant effects, prevents UV skin damage, stimulates hair growth, and inhibits hair loss. These effects have made it an area of interest in adding caffeine to sunscreens, shampoos, and conditioners.[6]