Is topical saw palmetto (serenoa repens) absorbed through the skin?

Topical Saw Palmetto Absorption Through the Skin

Topical saw palmetto (Serenoa repens) is not significantly absorbed through intact skin based on available evidence. The molecular characteristics of saw palmetto extract components and skin barrier properties limit its transdermal penetration.

Skin Barrier Function and Transdermal Absorption

The skin serves as a robust barrier against external substances, with transdermal absorption following specific pathways:

• Transepidermal routes: Either transcellular (through cells) or intercellular (through lipid matrix between cells) 1
• Appendageal route: Through hair follicles and glands, limited to particles <500 Da 1

For effective transdermal absorption, molecules generally require:

• Molecular weight less than 500 Da
• Intermediate partition coefficient between vehicle and membrane
• Low degree of ionization 1

Evidence Regarding Saw Palmetto Absorption

The FDA labeling for topical saw palmetto specifically indicates it is "for external use only" and should not be used on damaged or broken skin 2. This labeling suggests the product is intended for local effects rather than systemic absorption.

Studies examining topical saw palmetto have focused on its local effects rather than systemic absorption:

• A 2016 study on topical saw palmetto for male androgenetic alopecia demonstrated increased hair count and terminal hair count with topical application, suggesting local rather than systemic effects 3

• A case report documented sensitization to topical saw palmetto in a patient with androgenetic alopecia, indicating local skin reactions rather than systemic effects 4

Mechanisms of Topical Drug Delivery

According to the British Photodermatology Group guidelines, for optimal transdermal effect, a substance should:

1. Demonstrate maximum absorption at specific wavelengths
2. Penetrate deeper skin levels
3. Be evenly distributed throughout the target tissue
4. Show high target/normal tissue concentration ratio 1

Most topical formulations either:

• Remain on the skin surface
• Act as depot formulations
• Induce structural changes in the stratum corneum to facilitate absorption 1

Clinical Implications

When considering topical saw palmetto products:

• Safety: While generally well-tolerated topically, saw palmetto can cause local skin reactions in sensitive individuals 4

• Efficacy: Topical saw palmetto appears to work through local mechanisms rather than systemic absorption 3

• Formulation considerations: The vehicle used in topical preparations significantly impacts potential absorption - lipid vesicles or other penetration enhancers would be needed for meaningful transdermal delivery 1

Conclusion

Based on the available evidence, particularly the FDA labeling and skin barrier properties, topical saw palmetto is unlikely to be significantly absorbed through intact skin. Its effects appear to be primarily local rather than systemic, making it suitable for targeted skin and hair applications without significant systemic exposure.