Final answer:
Hyperkeratosis and xerophthalmia are caused by a deficiency in vitamin A, which is crucial for maintaining healthy skin, mucous membranes, and vision.
Step-by-step explanation:
Both hyperkeratosis and xerophthalmia are caused by vitamin A deficiency. Vitamin A deficiency can lead to a variety of health problems including keratomalacia, characterized by dryness of the eye, and hyperkeratosis, which refers to the thickening of the skin's outer layer. Xerophthalmia encompasses a spectrum of eye diseases resulting from vitamin A deficiency, ranging from night blindness to the complete drying of the eye.
Both conditions reflect the essential role vitamin A plays in maintaining healthy skin and mucous membranes, as well as its importance in vision. Conversely, excess vitamin A, or hypervitaminosis A, can cause symptoms like nausea, vomiting, and headache, demonstrating the necessity of maintaining proper vitamin A levels within the body.