Actually, it doesn't. According to a theory that is spreading across the Internet, this DIY test involves taking a cup of toothpaste and mixing it with a few drops of urine. If you're pregnant, the toothpaste will supposedly begin to foam.
hCG contains amino acids and toothpaste is composed of a chemical called calcium carbonate. On the one hand, it is true that the combination between calcium carbonate and acid causes the substance to foam due to the production of carbon dioxide and water. So, this theory suggests that the presence of hCG can indeed cause toothpaste to foam.
However, urine contains acids as well, and this is the reason why this home pregnancy test doesn't actually work. The acid in urine can cause the same reaction in the toothpaste whether you're pregnant or not.
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