No, massaging the back with castor oil or St. John's wort oil does NOT cause penetration into the lungs
Topical application of oils to intact skin on the back does not result in oil entering the lungs. This is a physiological impossibility through normal dermal absorption pathways.
Why This Concern is Unfounded
The lungs can only be exposed to oils through two mechanisms:
- Aspiration or inhalation - when oil droplets are breathed into the airways
- Injection - when oils are introduced directly into tissues or bloodstream
Topical Application is Safe
The FDA-approved labeling for St. John's wort oil explicitly designates it "For external use only" 1, with standard precautions about skin sensitivity—not lung penetration. The safety profile focuses entirely on dermal reactions (redness, irritation) 1.
Castor oil has extensive safety data showing it functions as a skin-conditioning agent when applied topically 2. A comprehensive safety assessment found castor oil is "not a significant skin irritant, sensitizer, or photosensitizer in human clinical tests" 2. The review examined dermal absorption and enhancement of transdermal penetration of other chemicals, but found no evidence of systemic distribution to lungs from topical use 2.
When Oils Actually Reach the Lungs
The only documented case of oil-related lung injury involved aspiration, not topical application. Lipoid pneumonia occurred in a patient who ingested Lorenzo's oil, which was then aspirated into the airways 3. This represents inhalation of oil droplets—a completely different exposure route than back massage.
Similarly, severe complications from castor oil occurred only after large-volume subcutaneous injection (500 mL injected into tissues), causing multisystem organ failure 4—again, not from topical application.
Clinical Bottom Line
Massage with these oils on intact back skin poses no risk of lung penetration. The skin barrier prevents oils from entering the bloodstream in quantities that would reach pulmonary tissue. Any therapeutic benefits or adverse effects remain localized to the skin and underlying soft tissues.
The only precaution needed is avoiding inhalation of aerosolized oil droplets if using spray formulations 2, which is irrelevant to massage application.