Wearing sweaters directly on the skin can cause itching, redness, or rashes for some individuals. Dermatologists explain this can be due to mechanical irritation from rough fibers like wool, particularly for those with sensitive skin or conditions like eczema. Allergic contact dermatitis to wool, dyes, or processing chemicals is another cause. Additionally, sweaters can trap heat and sweat, fostering bacterial or fungal growth leading to infections or heat rash. Irritation typically appears immediately and resolves quickly, while allergic reactions may develop over time with more severe symptoms.