The beauty industry has never been squeamish about dabbling in extremes. Think bird poop facials, vampire face lifts, snake and bee venom skincare, vagina steaming, and Korean face slapping, to name just a few.
This can also be seen in the use of high-low temperatures for aesthetic and wellness purposes, from sweat-inducing hot yoga and infrared saunas to the chilling processes of cryotherapy and fat-freezing.
And since most of us don't have the luxury of our own steam bath or cryo chamber at home, beauty brands have responded with both warming and cooling skincare products and DIY gadgets.
But when is it time to turn up the heat?
Some of these offerings are self-heating, such as Farmacy's Honey Potion Renewing Antioxidant Hydration Mask, which warms as it transforms into a creamy texture when massaged over skin.
Others are cold-temperature workers, like the Charlotte Tilbury Cryo-Recovery Face Mask, a reusable silicone mask studded with cooling metal beads to target acupressure points. It's intended to bring about firmer, more lifted and fresher-looking skin- simply pop it into the freezer 30 minutes before use.
Some electronic facial devices rely on gentle heat, not only to deliver a relaxing experience, but a more effective one too.
The Foreo Luna 3 Plus, for instance, boasts thermal powers that reportedly give you a more thorough face cleanse, while the Osim uGlow Eye promises brighter, more youthful peepers with its heated massage function that helps to boost microcirculation.
But beyond enjoying the immediate comfort these products deliver, how do we know if we should be turning up the heat or chilling out in our skincare routines?
According to Dr Kok Wai Leong, dermatologist at DS Skin & Wellness Clinic, heat therapy may be useful for wound healing as it boosts blood flow to the skin, bringing more oxygen and nutrients for skin repair.
"Heat also alleviates swelling in skin inflammation or infections. And there has been research to show that skin permeability increases with heating of the skin. Theoretically, this will increase the absorption of treatment products that are applied."
However, the circulation-boosting benefits of mild heat are likely limited. "Just like applying a hot towel on your face on the airplane or when you are in a hot sauna, you feel refreshed because of the increased blood flow to the skin and the opening of your pores, but such effects are short-lived," he explains.
Although there is no ideal temperature range at which skin-warming products are the most effective or comfortable — it varies between individuals — what's worth bearing in mind is that the application of heat should always be gradual and controlled.
"Unregulated use of heat-generating devices on your skin may lead to heat build-up, which causes skin irritation and inflammation instead of repair," says Dr Kok.
"In a real world setting, it is difficult to ensure that skin temperature remains constant. Over-heating or prolonged heating can occur, causing skin damage. And even with short-lived but rapid heating, thermal-related heat effects like burns and blisters may develop," he cautions.
Dr Low Chai Ling, founder of SW1 Clinic, also cautions that heat therapy is contentious at best, with its effectiveness dependent on the heat source, how long the skin is exposed and at what temperatures.
"Recent evidence indicates that infrared and heat may induce premature skin ageing, just like UV radiation. Not only do they degrade collagen and decrease collagen production, heat energy can also result in the development of solar elastosis," she says.
Solar elastosis is a disorder caused by sun damage, in which skin loses its elasticity and appears yellowed and thick.
Or, maybe it's better to chill out
On the other end of the thermometer, cold therapy comes in handy when you need to tackle skin inflammation, such as during breakouts of large, painful cystic acne, sunburn and irritation. Not only does lowering skin temperature inhibit inflammation, it has a numbing and soothing effect, so skin feels less raw.
Those prone to redness and rosacea will also benefit from a drop in the mercury, as cooling the skin leads to vasoconstriction — a shrinking of blood vessels. This means less blood to the skin and hence a reduction in redness, though Dr Kok says temperatures should not be varied too drastically, as aggressive vasoconstriction can lead to broken capillaries.
"Cooling products like sheet masks and massagers do temporarily relieve skin inflammation and itching. They also help to address dark circles and eye fatigue, which can be partially caused by vasodilation or enlargement of blood vessels in the skin around eyes," he says.
However, Dr Low warns that there are potential downsides to cold therapy too. She says: "In the short term, cold therapy may make skin look a little brighter and reduce redness due to the superficial vasoconstriction effect, but extreme cold can lead to rashes, frostbite and other issues."
Dr Kok adds: "There have been reports about the anti-inflammatory benefits and vasoconstricting action of cold therapy, but the effects are transient. While they may be useful in the short term for inflamed or sensitive skin, they should not be used as the main treatment."
In addition, cooling products may contain alcohol or menthol. The latter delivers a cooling sensation without an actual fall in skin temperature.
"These products may lead to evaporative water loss. They should be used together with a moisturising agent to prevent dryness or irritation," he explains.
This article was first published in Her World Online.