Which of the following is NOT a symptom of acute radiation exposure?

Loss of appetite is not typically recognized as a direct symptom of acute radiation exposure. Acute radiation syndrome manifests through immediate and observable physical effects following exposure to high doses of ionizing radiation in a short time period. The symptoms associated with this condition generally include hair loss, vomiting, and skin reddening, as these are the body’s acute responses to cellular damage caused by radiation.

Hair loss occurs due to the rapid turnover of hair follicles affected by radiation, which disrupts normal hair growth. Vomiting can be triggered by radiation's impact on the gastrointestinal tract, resulting in nausea and a significant gastrointestinal upset. Skin reddening, or erythema, signifies damage to the skin tissue, which can manifest as redness and inflammation after exposure.

Although loss of appetite can be a consequence of illness and may be associated with radiation exposure, it is not an immediate or definitive symptom of acute radiation syndrome compared to the other symptoms listed.