Which chemical is more caustic?

• A. Potassium Hydroxide
• B. Sodium Hydroxide
• C. Ammonium Thioglycolate
• D. Calcium Hydroxide

Answer: (B)

Caustic substances are corrosive and can cause severe burns to skin and eyes; in a salon, recognizing which chemicals pose the strongest burns helps you handle them safely. Sodium hydroxide is a very strong base and readily dissociates in water to produce a high concentration of hydroxide ions, which aggressively damage proteins and tissues. That combination of high reactivity and powerful causticity makes it the most hazardous among the options, so it’s identified as the most caustic. The other substances listed can be caustic as well, but they are not as aggressively caustic in typical salon-use conditions. Ammonium thioglycolate is a reducing agent used in perms and can be irritating in concentrated form, calcium hydroxide is a strong base but generally less aggressive in common uses, and potassium hydroxide is also highly caustic but is not the answer in this context. Always handle all caustic chemicals with proper PPE and rinse thoroughly if contact occurs.