Final answer:
Thickened skin with distinct borders caused by excessive scratching or prolonged irritation is referred to as eczema, which exhibits itchy, dry patches of skin. Another related condition is psoriasis, characterized by thick, red skin with silvery scales.
Step-by-step explanation:
Thickened skin with distinct borders, often resulting from excessive scratching or prolonged irritation is referred to as eczema. Eczema is a skin condition that manifests as dry, itchy patches resembling rashes, which may swell, flake, and in severe cases result in bleeding. Conditions such as psoriasis can also cause itchy or sore patches of thick, red skin with silvery scales, commonly affecting areas like elbows, knees, and scalp. While eczema is thought to be an allergic reaction, potentially linked to antibodies against dust mites, psoriasis involves a complex interaction between skin cells and immune cells, leading to rapid skin cell turnover.