One article on PainSci cites Park 2008: Does Epsom Salt Work?
PainSci commentary on Park 2008: ?This page is one of thousands in the PainScience.com bibliography. It is not a general article: it is focused on a single scientific paper, and it may provide only just enough context for the summary to make sense. Links to other papers and more general information are provided wherever possible.
This study showed that heating of the skin can dramatically increase it’s permeability. They tested primarily short bursts of intense heating: 5 milliseconds to 5 seconds, and 100 to 315 degrees Celsius. The more heat, the more molecules could cross; the duration of exposure had less effect. Skin permeability was increased by a few multiples in the low end of the range, all the way up to three orders of magnitude at the most extreme temperatures, which basically burns micropscopic holes in the surface of the skin, effectively creating artificial, temporary pores. (That sounds awful, but it’s actually painless, because the application of heat is so brief.) At lower temperatures, the increased permeability is due to disordering and disrupting the stratum corneum lipid and keratin structures, making them a less effective barrier.
~ Paul Ingraham
original abstract †Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.
Although the effects of long exposure >1s) to moderate temperatures (< or =100 degrees C) have been well characterized, recent studies suggest that shorter exposure (<1s) to higher temperatures >100 degrees C) can dramatically increase skin permeability. Previous studies suggest that by keeping exposures short, thermal damage can be localized to the stratum corneum without damaging deeper tissue. Initial clinical trials have progressed to Phase II (see http://clinicaltrials.gov), which indicates the procedure can be safe. Because the effect of heating under these conditions has received little systematic or mechanistic study, we heated full-thickness skin, epidermis and stratum corneum samples from human and porcine cadavers to temperatures ranging from 100 to 315 degrees C for times ranging from 100ms to 5s. Tissue samples were analyzed using skin permeability measurements, differential scanning calorimetry, thermomechanical analysis, thermal gravimetric analysis, brightfield and confocal microscopy, and histology. Skin permeability was shown to be a very strong function of temperature and a less strong function of the duration of heating. At optimal conditions used in this study, transdermal delivery of calcein was increased up to 760-fold by rapidly heating the skin at high temperature. More specifically, skin permeability was increased (I) by a few fold after heating to approximately 100-150 degrees C, (II) by one to two orders of magnitude after heating to approximately 150-250 degrees C and (III) by three orders of magnitude after heating above 300 degrees C. These permeability changes were attributed to (I) disordering of stratum corneum lipid structure, (II) disruption of stratum corneum keratin network structure and (III) decomposition and vaporization of keratin to create micron-scale holes in the stratum corneum, respectively. We conclude that heating the skin with short, high temperature pulses can increase skin permeability by orders of magnitude due to structural disruption and removal of stratum corneum.
This page is part of the PainScience BIBLIOGRAPHY, which contains plain language summaries of thousands of scientific papers & others sources. It’s like a highly specialized blog. A few highlights:
- Photobiomodulation therapy is not better than placebo in patients with chronic nonspecific low back pain: a randomised placebo-controlled trial. Guimarães 2021 Pain.
- No effect of creatine monohydrate supplementation on inflammatory and cartilage degradation biomarkers in individuals with knee osteoarthritis. Cornish 2018 Nutr Res.
- The CANBACK trial: a randomised, controlled clinical trial of oral cannabidiol for people presenting to the emergency department with acute low back pain. Bebee 2021 Med J Aust.
- Relationships Between Sleep Quality and Pain-Related Factors for People with Chronic Low Back Pain: Tests of Reciprocal and Time of Day Effects. Gerhart 2017 Ann Behav Med.
- Modulation in the elastic properties of gastrocnemius muscle heads in individuals with plantar fasciitis and its relationship with pain. Zhou 2020 Sci Rep.