I don't understand why you touched bleach with your bare hands to begin with. When working with bleach – use protective gloves. I even recommend wearing safety goggles, and I hope you will be convinced by the time you finish reading my reply.

Household bleach solutions, which contain 3-6% sodium hypochlorite (NaClO), are often perfumed to cover the unpleasant smell of the active chemical. Different soaps and detergents are also often added. As you know, soap is smooth to the touch, which probably explains at least some of the smooth sensation. However, this is not the only explanation, since simple bleach solutions, with no additives, cause skin smoothness. Sodium hypochlorite itself is not oily, therefore it is not the direct cause for the smoothness, which leaves the skin as the source for this sensation. I will explain:

In the following table (adopted from Wikipedia), the acidities of various materials are listed, according to the pH scale:

The pH scale represents the level of acidity or basicity, where 7 is neutral (distilled water). Values lower than 7 are considered acidic and indicate a high concentration of the H+ ion in the solution, whereas values higher than 7 are considered basic and indicate a high concentration of the OH- ion. The pH scale is logarithmic, meaning that the difference in the level of acidity (more precisely the concentration of the H+ ion) between two consecutive whole numbers is ten-fold. For example, a pH level of 3 is ten times more acidic than a pH level of 4. The same goes for basicity – pH 13 is ten times more basic than pH 12, and is a thousand times more basic than pH 10. As the above table indicates, bleach is one of the most basic household materials, second only to caustic soda (NaOH) which is used for clearing clogged drains and for producing soap from fats.

So what makes bleach so basic? Two reasons: (1) sodium hypochlorite is the salt of hypochlorous acid (HClO). As a weak acid, HClO tends to remain intact in an aqueous solution rather than break down into its ionic components and thereby release H+ ions. Thus, the salt of a weak acid, when dissolved in an aqueous solution, "steals" H+ ions from water molecules, thereby releasing OH- ions to the solution, increasing its basicity. In the case of sodium hypochlorite, the chemical reaction is this:

NaClO + H2O -> HClO + NaOH

As you can see, when sodium hypochlorite is dissolved in water, caustic soda (NaOH) is formed. However, according to the chemical reaction's equilibrium constants, the calculated pH of a sodium hypochlorite solution is 10.6, not the measured 12.5 (which is almost 100 times more basic). This discrepancy is explained by the second reason: (2) manufacturers add to the bleach solution up to 1% caustic soda, which stabilizes the bleach and prevents it from releasing chlorine gas through a chemical reaction which is the reverse of the bleach production reaction:

Cl2 + 2 NaOH <---> NaCl + NaClO+ H2O

Of course the reverse reaction is not completely blocked, as bleach solutions do have a typical chlorine gas (Cl2) smell.

A strong basic environment such as that in bleach drives hydrolysis reactions – breakdown of molecules by water. Molecules that can be hydrolyzed such as fats, which break down into glycerin and fatty acids (this is how soaps are made), proteins which are hydrolyzed into their amino acid components and complex sugars which break down into their monosaccharide components.

And now that we went through all the relevant explanations, we can understand why bleach turns our skin smooth and oily:

Layers of the skin. Layer 1 is made of dead cells (adopted from Wikipedia)

The outermost layer of our skin (the outer layer of the epidermis) is made of dead cells. Dead cells are composed mostly of proteins, fats and sugars. Touching bleach sets forth a hydrolysis reaction of our hand. This means that the oily sensation you feel is actually the top layer of your skin beginning to break down and dissolve! Luckily, the skin on your hand is rather thick, and the bleach usually doesn't penetrate deep enough to harm living cells (which is when a painful chemical burn occurs). Click here to see a picture of a chemical burn caused by bleach penetrating the gap between this poor person's ring and finger. Trust me that I avoided publishing links to more graphic pictures of chemical burns caused by bleach or other strong bases.

I hope that you are now convinced that it is highly recommended to wear gloves, and even safety goggles, when working with bleach.

Dr. Avi Saig
Department of Neurobiology and the Davidson Institute
Weizmann Institute of Science
 
A note to the reader

If you find these explanations insufficiently clear or if you have further questions on this topic, please write about this in our forum, and we will relate to your comments. Your suggestions and constructive criticism are always welcome.

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