Both of these hydroxide substances are extremely corrosive in solid or liquid form. Any contact with the body in any form can cause severe damage in the form of slow healing burns. Breathing in the dust of either of them can cause lung damage. Though both caustic substances have similarities and can often be used interchangeably, they have some distinct differences.
Potassium Hydroxide is slightly more corrosive than Sodium Hydroxide making it slightly more physically dangerous. Be aware also that it is more highly soluble in ethanol or methanol than Sodium Hydroxide. When dissolved in water, Potassium Hydroxide gives off more heat than does sodium hydroxide. Use heat proof containers. The reaction in water is strong so always add it to water and not the other way around so that a volcanic reaction does not occur. Potassium Hydroxide will snap and crackle as it dissolves in water, unlike Sodium Hydroxide.
Though some of these differences are slight, they are significant enough that should a scientist perform an experiment without knowing the differences, there is a possibility of danger.
It depends upon handling the substance in solid or dissolved form. When dissolved in water, both behave in a similar manner. They are caustic (basic), corrosive, and can be incredibly harmful to the human body. Sodium hydroxide (NaOH) and potassium hydroxide (KOH) both containing a single -OH group that makes them dangerous. The Na+ and K+ ions are both relatively harmless for a person as both are essential electrolytes needed to maintain homeostasis. It's the OH group that is responsible for the dangerousness of the solution and, assuming equal concentrations, are equally harmful.
However, when in solid form, NaOH is likely more dangerous. It is an incredibly hygroscopic substance, pulling moisture from the air to produce a solution whereas potassium hydroxide is much less active. Further, if both are actively dissolved in water, they each will release some thermal energy (heat). Sodium hydroxide will releases significantly more energy when dissolved it could possibly ignite some adjacent combustibles.
Sodium Hydroxide, called lye and Potassium Hydroxide, also called caustic potash have some common properties: both are caustic, corrosive and highly hazardous
Physical dangers of Potassium Hydroxide
Potassium hydroxide is a highly corrosive chemical and contact can severely irritate and burn the skin and eyes leading to eye damage
Contact can irritate nose and throat.Inhaling Potassium hydroxide can irritate lungs and higher exposure may cause build up of fluid in the lungs (pulmonary edema).
Exposure to Potassium hydroxide can cause headache, dizziness vomiting and nausea and may cause a skin allergy.
Physical dangers of Sodium Hydroxide
Sodium hydroxide is a highly corrosive chemical and contact can severely irritate and burn the skin and eyes with possible eye damage.
Contact can irritate mouth, nose and throat. Inhaling can irritate lungs and higher exposure may cause build up of fluid in the lungs (pulmonary edema). Repeated exposure can lead to permanent lung damage
Sodium hydroxide in contact with water or moisture generates enough heat to ignite combustibles.