To determine which option is a direct health effect of prolonged exposure to high levels of noise pollution, we need to understand the potential impacts of noise pollution on human health.

Noise pollution is unwanted or harmful sound that can affect human health and environmental quality. One of the most significant health concerns related to noise pollution is its effect on the cardiovascular system, including:

• Elevated Stress Levels: Prolonged exposure to high levels of noise can increase stress hormones like cortisol and adrenaline.
• Impact on the Cardiovascular System: The increased stress levels and hormone secretion can lead to an increase in heart rate and blood pressure.

Given these points, let's evaluate the options:

1. Improved memory: High noise levels do not improve cognitive functions; they are more likely to impair concentration and memory.
2. Increased appetite: Noise pollution is not known to significantly affect appetite.
3. Skin irritation: Noise itself doesn't cause skin irritation; this is more likely due to chemical or physical factors rather than auditory ones.
4. High blood pressure: As explained above, this is a well-documented effect of prolonged exposure to noise pollution due to increased stress responses and impacts on the cardiovascular system.

Conclusion: The correct answer is High blood pressure, as this is a direct health effect of prolonged exposure to high levels of noise pollution.

Understanding these effects is crucial for environmental engineering, as controlling noise pollution contributes significantly to public health and safety.