**Core Concept**
The ear's vestibular system is sensitive to temperature changes, which can cause caloric stimulation, affecting balance and equilibrium. This is due to the temperature difference between the cold water and the inner ear fluid, triggering the vestibular apparatus.

**Why the Correct Answer is Right**
Caloric stimulation occurs when a temperature difference between the external ear canal and the inner ear fluid affects the vestibular apparatus. This happens because the temperature of the cold water causes a convective current in the endolymph of the semicircular canals, which in turn stimulates the vestibular hair cells. This stimulation can cause nystagmus, vertigo, and balance disturbances. The correct answer, "Caloric stimulation caused by cold water," highlights the importance of avoiding temperature changes in ear cleaning to prevent vestibular symptoms.

**Why Each Wrong Option is Incorrect**

**Option A:** It will make the wax hard. While cold water can harden earwax, this is not the primary reason for avoiding its use in ear cleaning. The ear's vestibular system is more sensitive to temperature changes than earwax composition.

**Option B:** Damage to tympanic membrane. Cold water is unlikely to cause direct damage to the tympanic membrane. The tympanic membrane is more susceptible to damage from foreign objects, excessive pressure, or infections.

**Option D:** It will cause infection. There is no direct link between using cold water for ear cleaning and causing an infection. In fact, proper ear cleaning can help prevent infections by removing excess earwax and debris.

**Clinical Pearl / High-Yield Fact**
When performing ear cleaning, use warm water to avoid caloric stimulation and ensure patient comfort. If the patient experiences vertigo or nystagmus during ear cleaning, stop immediately and consult a healthcare professional.

**✓ Correct Answer: C. Caloric stimulation caused by cold water**