Red, swollen and hard neck pimples can be caused by acne and boils. 1. Acne: Acne is mainly related to the increase of androgen levels and sebum secretion, and is most common on the face, but can also involve the neck, forehead, back and shoulder blades. When acne is triggered in the neck, it will cause hard red pimples to appear on the surface of the skin. 2. Boils: Boils are mostly caused by Staphylococcus aureus infections, and are found on the face, neck and buttocks. They are mainly characterized by one or more red hemispherical nodules on the skin surface, which are hard and accompanied by symptoms such as redness, swelling, heat and pain. Neck acne red swelling hard may also have other causes, it is recommended to go to the hospital in a timely manner to improve the examination, to clarify the cause of the disease to give targeted treatment.