Skin is a physical barrier to keep intruders out. It doesn’t like loiterers, either. Skin effectively attacks all kinds of microbes and germs at the skin surface. It secretes antimicrobial peptides with waxy stuff called sebum. Sebum is a good sealant – it helps build the wall, reducing skin permeability and keeping good in and bad out. It’s also an acidic lipid, which makes the skin less than hospitable for intruders. The acidity is called the acid mantle.
Sebum isn’t all good. Like a lot of things relating to the skin, hormones control sebum production…which is why sebum levels sometimes go out of control at puberty. And too much sebum is not a good thing: it is such a good sealant, it locks everything in, including dirt, and is closely linked with acne. Too little ain’t so great, either, since the acid mantle is an essential defense against intruders.
So what does bathing and soap have to do with sebum? Lots.
Soap can cause havoc. It affects the acid mantle in two ways: First, surfactants strip the skin of sebum and other important natural lipids by binding to proteins. Second, the alkaline pH of soap can interfere with the normal acid barrier, raising the pH (e.g., 5.5 to 7.5), and making infection and cracking, fissured skin more likely.
Not only that, skin pH effects the normal shedding process. The dead skin cells normally degrade and shed under acidic conditions. When the skin’s acid mantle is impaired, the natural exfoliation process gets impaired as well…which can lead to scaly xerosis. The skin is very good at repairing itself, and can usually correct the damage after a few hours, BUT chronic washing, say 10 times a day, can permanently alter the acid mantle. Seriously, wash carefully!
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