There is no secret. The Dead Sea is the lowest place on earth and the water in the sea contains more salt than any other body of water.
It is not only the fact that there is more salt; the salt of the Dead Sea contains only 12 to 18% of sodium salt while the normal chloride ocean contains more than 97% of sodium chloride. This is one reason why its salt is so beneficial. You can also look for dead sea products via https://www.armanigallery.com.au/category/dead-sea-minerals/.
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The ancient Egyptians were blown away by the salt and they have developed several soaps and skin creams and they are the predecessors of the Dead Sea products on the market today. Bath salts, body wraps, foot scrubs, and cosmetics have roots in ancient elixirs used by Egyptian royalty and other wealthy travelers regions.
The world has discovered the shocking qualities of this salt there for thousands of years and the benefits of the use of today using similar products reduce deep wrinkles in the skin, and some of them help to alleviate the symptoms of different types of arthritis.
The high concentration of bromide and magnesium in some of these products to reduce allergic reactions by detoxifying and cleansing of the skin.
Skin conditions like acne and psoriasis are relieved by soaking in salt and products that contain a high concentration of magnesium from this salt reduce inflammation and improve skin hydration.