What is the skin acid mantle?
The skin acid mantle is the layer between the epidermis (the epidermis, and the skin secretions, such as perspiration.) The healthy mantle has a pH of between 4.5 and 5.75, and serves as the first protection against microorganisms.
What is a pH?
The pH is a chemical scale to divide acids and bases, due to their strength. The abbreviation pH stands for the Latin "potentia hydrogenii", which means something like "The power of hydrogen (potentia - power, force, hydrogenii - (des) hydrogen (s))". The pH is a scale of 0-14, which indicates the ratio of hydrogen ions (H +) or oxonium ions (H3O +) and hydroxide ions (OH-). A pH below mid-point 7 is acidic (ie 0-6) and a pH above 7 is basic (8-14). In addition, the scale becomes exponentially larger because with each one-digit change, the concentration of the particular particle increases increased by 10 times. 
→ A pH of 7 indicates the middle of the scale, here the amount of H + and OH- is equal to 1: 1 - e.g. Water has a pH of 7. It is considered neutral
→ A pH value of 6 is acidic, so that the amount of H + increases tenfold, the ratio is now 10: 1 - mineral water is slightly acidic with a pH of 6
→ If you now go to a pH of 5, the ratio is 10 × 10 to 1, ie 100: 1. At a pH of 4 therefore 100 × 10 to 1, ie 1000: 1 and so on. - Coffee has a pH of 5 and wine a pH of 4.
→ This also goes in the other direction, so a pH of 8 in the ratio 1:10, a pH of 9 1: 100, etc. - seawater has a pH of about 8 and soap one of about 9
When you hear the word "acid" or "base" you immediately think of the worst of the worst. But the corrosivity of acids and bases are dependent on many factors. Thus, pure acetic acid is highly corrosive to metals, and causes severe burns, diluted to 3-12%, we find them in the household for cooking, and diluted to the 30% as a detergent. Also, while pH is not always the key, hydrofluoric acid (HF) is not as strong a acid as hydrochloric acid (HCl), but the fluorine particle causes much worse, damage, much quicker than the chlorine particle.
What is the significance of pH in the human organism?
In different areas of our body, we need different pH levels to perform important functions. Thus, e.g. because hemoglobin in the blood absorb less oxygen in acidic conditions, in basic then more. Acidification of the blood - acidosis - or under-acidification of the blood - alkalosis - has a negative effect on blood pressure. In the stomach is hydrochloric acid, with which we decompose food. There we find a pH of 1-4, depending on the time of day and diet. Our saliva is also acid to neutral, depending on the time of day and diet.
What significance does the pH have on the skin?
The pH that is present on the skin is part of our natural defense. It helps kill harmful microorganisms and keeps our natural skin flora alive. In general, it is slightly lower in men than in women, in babies slightly higher (about 5.5 - 6.5), as this protection is not yet fully developed. The skin flora is a complex mixture of different microorganisms, ie bacteria and fungi. They sometimes help to preserve the protective mantle by converting fats to fatty acids, thereby killing other, worse pathogens (corynebacteria), or giving us humans our individual body odor (Brevibacterium). Basically, they are harmless, but for people with intact immune systems, for people with immune system disorders, they can lead to diseases and inflammation (streptococci). Generally, one distinguishes between bacteria that are alkaliphilic and acidophilic. Too high a pH on the skin can lead to diseases such as dermatitis, seborrheic eczema, or infectious diseases. In turn, too low a pH can cause redness, irritation and dryness.
Should you use acid, skin neutral, or basic cosmetics?
First of all, the word "skin neutral" is often misunderstood, because it does not mean that a product has a pH of 7 (chemically neutral), but a 4.7-5.5. So a pH neutral product is not chemically neutral, but neutral in relation to the pH of the skin. In healthy people, it does not matter what pH a cosmetic product has. The effect of each article determines their pH, so creams are mostly acidic, shampoos and soaps mostly basic. The skin acid mantle returns to its original level after only a few hours. People with disease conditions are more susceptible now and again to the fact that the pH does not recover so quickly.
The controversy surrounding the skin acid mantle
The opinions differ here, whether the skin acid mantle is just a great advertising trick of the industry, or more. It is not agreed, since you could not make a 100% statement to the benefit of the coat. As a counter-argument, there is the "hyperacidity", this is about our body has too many acidic media, and these are removed via the skin. However, this theory has not been proven, and is often used as an argument by Naturopaths, and Alternative Medicine application, if not the last to sell their products. So far we cant say exactly who is wrong and who is right.
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