The restorative powers of the sea have seeped into the medical traditions of almost every culture. From the magical virtues bestowed on the thermal springs of ancient Greece to the practice of thalassotherapy that runs through France, salty seawater is synonymous with sustaining life. And while our sources of this precious commodity are considerably more polluted than they used to be, our collective belief in healing properties of seawater persists.

Folk medicine and modern science both point to seaweed as a concentrated source of rehabilitative potential. The greeny-brown nuisance that floats to the surface of the water like a stray plastic bag and wraps itself around your toes: that’s the good stuff. The slime that clings to jagged rocks, patiently waiting for you to lose your balance in a moment of slapstick sadism? Also good.

Those lonely fronds that wash up on the shore betray the true power of seaweed. Approximately 36 per cent of seaweed’s dry mass consists of minerals drawn from the deep blue. These include sodium, calcium, magnesium, potassium and phosphorus, not to mention micronutrients iodine, zinc and copper along with 20 amino acids. It boasts 13 vitamins, including vitamins C, A and B12. Seaweed is an antioxidant, an antiseptic and an anti-inflammatory.

When ingested, seaweed helps strengthen the gut wall, detox the body and assist in the proliferation of good bacteria (bizarrely, there is a study examining the faecal flora of Japanese women to prove this last point). When used topically, it manages to heal wounds while offsetting stress, pollution and, studies now reveal, the visible effects of ageing. Gaze beneath the surface of the water and the power of seaweed becomes clearer. In situ, ribbons of bottle-green glass dance elegantly with marine life, their delicate tendrils clinging to the rocks beneath them.

The real power of multicellular algae lies in its ability to self-regenerate in extreme and constantly changing environments. Instead of withering away and dying, seaweed remains indestructible and resilient. So imagine what it can do for your face.

Seaweed has found its way into countless skincare products. It is so popular that, according to market researchers at Mintel, two per cent of bodycare products launched between 2011 and 2015 contained the key ingredient.

Among these brands is Ren Skincare, which has included Atlantic kelp and algae in a new bodycare line that builds on the success of its cult Seaweed And Sage Body Wash. The products are a kind of renewable energy in that they restore the body’s levels of magnesium and other trace elements while supporting cell activity. Elsewhere, Elemis, Thalgo, The Body Shop, Lancôme and even niche brands such as Living Sea Therapy and Voya have created results-driven formulas around seaweed.

The most famous brand to harness the power of the sea is La Mer (the clue is in the name). In what sounds like the beginnings of a Marvel comic, the La Mer founder, an aerospace physicist named Dr Max Huber, sustained chemical burns to his face while conducting experiments in his laboratory. He swiftly set about developing a remedy, using brown seaweed kelp as a base.

The kelp underwent a four-month bio-fermentation process that turned it into Miracle Broth, a powerful catalyst for skin regeneration that became the foundation of the brand. Dr Huber’s burns were healed, and La Mer was born. That same broth can be found in the brand’s hero products, including The Moisturising Gel Cream and The Concentrate. La Mer is so protective of the kelp it uses that it hand harvests only the top fronds and ships them to its labs at once, so that its integrity is preserved.

While super-actives come and go like fashion trends, clinical evidence will ensure seaweed has a long future in skincare. One variety, Fucus vesiculosus (bladder wrack), has been proved to reduce wrinkle depth and age spots while boosting skin brightness. Undaria pinnatifida (wakame) has similar properties, but with the added bonus of improved moisture retention. It also reduces redness after UV exposure and activates genes associated with wound healing.

Experiments have demonstrated that both species are able to activate the SIRT1 protein, a sirtuin that has been linked to longevity in mammals. It has been touted as the anti-ageing gene on account of its ability to preserve the lifespan of a cell. It is the one bio-regulator for ageing that the entire beauty industry is attempting to control and, it turns out, these species of seaweed might play a central role.

Ninety-five per cent of the world’s supply of seaweed comes from Asia, where it has a long tradition as a medicine, skincare active and culinary staple (peruse the menu of a sushi bar and you’re likely to come across arame, hijiki, nori and wakame). Most cosmetic companies import their seaweed from Japan for this very reason.

Less exotic, but equally abundant in seaweed, are the coastlines of Scotland, Ireland and even Margate in Kent, the seaside home of grooming brand Haeckels. The tidal conditions and consistent sea temperature of the British Isles make the coastlines an ideal home for marine algae.

And just like Asia, there is a long but largely unknown tradition of seaweed-based therapies. They were most likely prompted by the words of 18th-century physician Dr Richard Russell, who prescribed that “one must drink sea water, bathe in it and eat all manner of marine life in which its virtue is concentrated”.

In Ireland, seaweed baths were routinely prescribed for the elderly as a remedy for arthritic joints and rheumatism. The practice was so common that, by the beginning of the 20th century, there were 300 seaweed bath houses dotted around the country. In Scotland, seaweed was used in poultices and vermifuges (agents that expel parasitic worms from the intestine). British history even has a host of culinary treats that contain seaweed. Welsh laverbread, for example, is a curious mix of boiled seaweed combined with oatmeal that has been fried in bacon fat.

Today, filmmaker-turned-volunteer beach warden Mr Dom Bridges holds one of only two licences to harvest seaweed from the English coast and plays a key role in the UK’s seaweed revival. Sourcing ingredients from a 20-mile radius of his laboratory in Margate, Mr Bridges developed the Haeckels brand after he grew weary of a career making ads for TV. The chalky coastline that surrounds his base nourishes varieties of seaweed that aren’t found anywhere else in the world. From them, he has created a range of products, including an Eco Marine Extract Facial Cream and Seaweed Facial Masque, now available on MR PORTER.

Demand for seaweed has skyrocketed over the past half-century and is only likely to grow. Analysts have suggested that seaweed could even become the future of UK farming. Beyond its health and skin benefits, it can be used as feed for animals and is a fantastic fertiliser. The amount of research into algal biofuel technologies is driving the need for seaweed aquaculture in the UK. One day in the distant future, the British coastline may be able to produce seaweed commercially but, for the time being, harvesting it is a labour-intensive process that hinges on preserving ecology while collecting only the finest species.