**Core Concept**
Hot flushes are a common symptom experienced by many postmenopausal women, characterized by sudden feelings of heat, sweating, and flushing of the skin. This phenomenon is primarily influenced by the hormonal changes that occur during menopause.

**Why the Correct Answer is Right**
Hot flushes are a result of the interplay between two primary factors: the decrease in estrogen levels and the increase in noradrenaline (norepinephrine) activity. Decreased estrogen levels lead to a reduction in the production of neurotransmitters such as serotonin and acetylcholine, which are responsible for regulating body temperature. This decrease in neurotransmitters results in an increase in noradrenaline activity, which in turn stimulates the hypothalamus to increase body temperature, leading to hot flushes. The combination of increased noradrenaline and decreased estrogen is thought to be the primary mechanism behind hot flushes.

**Why Each Wrong Option is Incorrect**
**Option A:** Increased noradrenaline alone is not sufficient to cause hot flushes, as it is the combination of hormonal and neurotransmitter changes that leads to this symptom.

**Option B:** Decreased estrogen alone can contribute to hot flushes, but it is the combination of decreased estrogen and increased noradrenaline that is thought to be the primary mechanism.

**Option D:** Increased noradrenaline and estrogen is not a plausible combination, as estrogen levels typically decrease during menopause, not increase.

**Clinical Pearl / High-Yield Fact**
Hot flushes can be alleviated with hormone replacement therapy (HRT) or selective estrogen receptor modulators (SERMs), which can help regulate estrogen levels and reduce noradrenaline activity.

**✓ Correct Answer: C. Increased noradrenaline and decreased estrogen. This combination is thought to be the primary mechanism behind hot flushes in postmenopausal women.**