What method can be used to remove red stains from a cashmere shirt?

To effectively remove red stains from a cashmere shirt, using alkaline solutions is a suitable method. Alkaline solutions, which typically consist of substances with a pH greater than 7, can help break down certain types of stains, particularly those from organic compounds, like those found in food, beverages, or biological materials. Their chemical properties can help lift the stain from the fibers of the fabric without causing damage.

In the case of delicate materials like cashmere, it's essential to choose an alkaline solution that is gentle enough to avoid harming the fibers. It's also important to follow the manufacturer's care instructions for the garment to ensure that the cleaning process does not lead to shrinking or other damage.

While the other methods mentioned may have their uses, they are not as effective for red stains specifically. Acidic solutions could potentially react negatively with the dyes in the fabric, while cold water may not be sufficient to lift the stain completely. Heat treatment can set stains into the fabric, making them harder to remove. Thus, alkaline solutions are the most effective choice in this scenario.