Waking up with a sore throat can be caused by several factors including dry air, dehydration, mouth breathing, allergies, acid reflux, and snoring or sleep apnea. Dry or cold air, especially in low humidity environments or when using air conditioning or heating, can dry out the throat tissues overnight, causing irritation. Breathing through the mouth due to nasal congestion or habits like snoring also dries and irritates the throat. Acid reflux, where stomach acid comes up into the throat during sleep, can cause a burning sore throat. Allergies and postnasal drip contribute by irritating the throat as well. Lastly, infections (viral or bacterial) are another common cause of a morning sore throat. If mouth breathing or snoring is a factor, it often makes the throat feel dry and sore on waking. Dehydration from not drinking enough water before bed or certain medical conditions can worsen symptoms. Lifestyle factors such as smoking, alcohol use, and voice strain may also play a role.

In summary, a sore throat upon waking is usually due to throat dryness and irritation from environmental or physiological factors like dry air, mouth breathing, reflux, or infections.