Which of the following skin conditions can be exacerbated by using harsh alkaline products?

Using harsh alkaline products can disrupt the natural pH balance of the skin, which is typically slightly acidic. This disruption can lead to irritation and sensitivity, particularly in individuals with rosacea. When the skin's barrier is compromised by alkaline substances, it may trigger an inflammatory response, worsening the redness, flushing, and general discomfort associated with rosacea.

In contrast, while acne can also be affected by the pH of products, it is more directly related to sebum production, bacteria, and clogged pores. Hyperpigmentation is usually influenced by sun exposure and skin trauma rather than product pH. Allergic reactions can occur from various substances, but they are not specifically linked to the use of alkaline products in the same way that they impact rosacea. Therefore, the connection between harsh alkaline products and the exacerbation of rosacea makes this condition the correct answer for the question.