Why we feel pain when we "touch" strong acid? It's because our skin is starting to dissolve? And the same thing to hydroxides (NaOH for example) - Why ?
Strong acids and bases are corrosive and can cause chemical burns to the skin. The exact manner and extent of the damage depends on the acid or base in question, but they can all react with organic compounds in the skin. They also usually damage the many nerve endings in the skin, causing the sensation of pain.
Acids react with and damage proteins in the skin, causing tissue damage. Some, such as sulfuric acid, are also strong dehydrating agents, capable of dehydrating carbohydrates in the skin and producing extra heat, which can lead to thermal as well as chemical burns. Hydrofluoric acid is even nastier - it interferes with nerve function, meaning that its burns are initially painless. However, it can diffuse through the skin more easily than many other acids, and the liberated fluoride ions can react with calcium in the bones, causing excruciating pain and irreversible damage. Contact with not much more than 100cm3 has been documented as fatal.
Bases also react with organic compounds in the skin - they can also react with proteins and damage them, but additionally they can saponify fats. Saponification is the name given to the process and reactions that produce soap; this process allows deeper penetration, so alkali burns tend to be more serious than many acid burns.
References & Further Reading:
Chemical Burns - Pathophysiology & Treatment
Chemical Burns - Medscape
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