What is a common sign of scalp irritation?

Redness and itchiness are common signs of scalp irritation as they indicate inflammation or an allergic reaction in the skin on the scalp. When the scalp is irritated, the body's immune response can cause increased blood flow, leading to redness, and the nerve endings can become sensitive, resulting in an itchy sensation. These symptoms often occur due to various factors such as product buildup, allergic reactions to hair care products, or underlying conditions like eczema or psoriasis.

Dull hair might suggest a lack of moisture or nutrients, but it does not specifically indicate irritation of the scalp. Excessive oiliness could be a result of overactive sebaceous glands, but it alone does not signify irritation; it can be a normal variation in skin type. Increased hair growth is typically influenced by hormonal factors rather than scalp irritation, so it does not correlate with the signs of irritation. The presence of redness and itchiness is a clearer indicator of scalp issues, making it the correct answer in this context.