Why do I have a sweet taste in my mouth?

Tasting something with nothing in your mouth is called phantom taste, which the NIDCD says is the most common taste disorder. A sweet phantom taste is less common than metallic or bitter, and it has fewer, but more important, explanations, because high blood sugar is one of them. Cleveland Clinic describes dysgeusia as a condition in which foods may taste sour, sweet, bitter or metallic, with causes ranging from infections and medicines to vitamin deficiencies.

• Acid reflux. Cleveland Clinic notes reflux can cause a sweet taste, often most noticeable at night when stomach contents and saliva enzymes reach the mouth.
• Sinus and respiratory infections. Inflammation from viral or bacterial infections affects smell and taste.
• Overnight dry mouth. Saliva that dries during sleep can make water taste sweet in the morning.
• Your water or cup. Well water high in calcium and iron, water from old pipes, or soap residue on a cup can all change taste.
• Medicines and other causes of dysgeusia, including infections such as COVID-19.
• High blood sugar and diabetes. Cleveland Clinic describes a persistent sweet taste as a potential sign of diabetes, because blood sugar regulation is disrupted.
• Diabetic ketoacidosis. DKA causes a sweet, fruity smell on the breath, which can also be experienced as a sweet taste.

The NHS lists the most common symptoms of diabetes as feeling thirsty all the time, peeing more than usual, feeling very tired and losing weight without trying, and advises an urgent GP appointment if you or your child have any of them. Check this list against how you feel:

A new sweet taste is a reason to check your blood sugar, and ketones if your care team has told you to. The NHS advises emergency care if blood ketones are over 3 mmol/L, if you have DKA symptoms and cannot check, or if you have DKA symptoms and have never been diagnosed with diabetes. MedlinePlus lists fruity-smelling breath, deep rapid breathing, nausea and vomiting, stomach pain, dry mouth, frequent urination or thirst lasting a day or more, and decreased alertness as DKA symptoms. Our page on fruity and acetone breath explains ketosis and DKA in more detail.

• For reflux, leave at least four hours between your last meal and bed, as Cleveland Clinic suggests, and raise the head of the bed.
• If only water tastes sweet, try a different glass, a filter or bottled water to rule out the water itself.
• Keep up normal brushing and tongue cleaning, which removes bacteria that can add to odd tastes.
• If the taste lasts more than a few days with no clear cause, see a doctor. A simple blood test checks your blood sugar, and an ear, nose and throat specialist can examine smell and taste if diabetes is ruled out.