In terms of therapeutic effects, the benefits of heat have been known for centuries, whether it is a sauna to cleanse and detox the body or a hot bandage to reduce inflammation. There is something simple and instinctive about warming a damaged part of the body. Modern techniques used in physiotherapy and rehabilitation rely on heat (e.g. ultrasound, diathermy) to reduce stiffness, improve circulation, reduce inflammation and promote a variety of physiological responses that speed up healing. This kind of tissue repair has parallels across many medical sectors, including wound healing, which in turn can be physiologically compared to more cosmetic anti-aging treatments, like increasing cellular population, the expression of proteins such ascollagen and vascularization.
Skin is known to become increasingly avascular and acellular with age and displays a progressive loss of proteins such as collagen and fibrillin, all exacerbated by cumulative sun exposure. There is also an overall atrophy of dermal tissue from a reduction of intercellular proteoglycans and subcutaneous fat, leading to a net loss of volume and turgidity. So, where does heat come in?First, let’s take a look at a few of the well-accepted anti-aging treatments that claim a rejuvenating effect:
• Light: laser, intense pulsed light (IPL), LED
• Acoustic: ultrasound
• Electromagnetic: radio frequency/thermage (RF)
The first group of light-based therapies is not only used in anti-aging, but also in hair removal. For a given intensity, the wavelength of the light will determine how deep the light penetrates into the skin and can therefore be used to target different depths. Chromophores in the skin (or hair) absorb this light and ultimately convert this form of energy into heat where it has a therapeutic effect, such as stimulating the expression of collagen and certain cytokines. In addition, ittriggers a heat shock protein response which, if controlled, is thought to have an adaptive effect on cells, making them more resistant to environmental stress. Similarly in hair removal, light is absorbed (best by darker hairs) and converted to heat, damaging the hair bulb and leading to a significant delay and net reduction in hair growth. Use of both broad spectrum light sources and wavelength specific ones rely on this conversion of one energy type, light, into another, heat.
Ultrasound is much the same; therapeutic ultrasound has been used in physiotherapy for over 50 years and its therapeutic effect relies on the absorption of acoustic energy by tissues highly concentrated in protein, such as tendon, ligament and bone. Skin has a protein content even higher than muscle, and therefore absorbs acoustic energy well, especially in the ultrasound region. Scar tissue typically has a higher collagen content than surrounding tissue and absorption of ultrasound in scars helps to increase its flexibility and extensibility. As a general rule, a higher frequency will allow for a quicker conversion to heat and a shallower ultrasound penetration. Frequencies of 3-5MHz are typically chosen to heat tissues, reduce inflammation and increase blood flow which speeds up healing. Lower frequencies penetrate deeper but are also eventually converted into heat, albeit less efficiently, and can also deliver substances into and across the skin by causing a mechanical cavitation effect in the stratum corneum, opening up channels for transdermal delivery.
Continuing through the list, it will be no surprise by now that radio frequency energy is used to... yes, heat tissue!Also known as diathermy and dielectric heating, RF often exists in beauty treatments under the name ‘thermage’ to provide a volumetric heating effect that ultimately stimulates a collagen expression leading to a net increase in skin volume and some degree of restoration to skin tissue. In the case of RF, the energy is high frequency alternating electric and magnetic fields that are absorbed by polar molecules such as water causing movement and manifesting this kinetic energy as heat. As with light and ultrasound, RF is non-invasive and is therefore popular with customers as there is usually no down-time for the patient. Like ultrasound, it can also be focused on a target point which minimizes damaging effects to the outer layers of skin through which it initially passes, only concentrating in intensity at the depth where it is needed. This is typically in the underlying dermis to stimulate collagen expression, or the deeper hypodermis to reduce the fat content of adipocytes in body shaping/sculpting treatments.
So, at a molecular and cellular level heat most definitely has a beneficial effect, while at a higher customer experience level, heat is growing in popularity. Spas and salons are increasingly offering heat as an option–from Turkish baths to monsoon showers, and heated stones to hot mineral masks. The effects of heat are being recognized all around and it is certainly something that can be used a lot more in the personal care space.
About the author
Dr. Peter Luebcke is a specialist senior technology consultant at Sagentia in the field of consumer products with particular focus in the personal care sector.Peter has first-hand experience leading a personal care products start-up and was intimately involved in both the design and development of products that fall into the blurred interface of consumer products and medical devices. He also has extensive biomaterials, engineering R&D project management and technology commercialization experience. Sagentia is a global innovation, technology and product development company that provides outsourced R&D consulting to start-ups through to global market leaders in the medical, industrial and consumer sectors.
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