While a thin tongue may suggest dehydration or malnourishment, a thick tongue may indicate fluid retention, malnourishment, or underlying health conditions including thyroid difficulties. A normal tongue is neither excessively thick nor too thin. Although a professional diagnosis is required for absolute accuracy, the thickness of a tongue, occasionally with scalloped edges, can reveal information about a person’s general health and degree of hydration.

Swollen or thick tongue

Look: bloated, puffy, and possibly with tooth indentations or scalloped edges.
Possible reasons:
retention of fluids.
malnourishment or deficits in nutrition.
various diseases or allergic reactions.
hypothyroidism.
excessive tongue tissue growth in certain situations due to diseases like acromegaly.

Tongue that is thin
Looks extremely little or narrow.
One possible reason is dehydration.
undernourishment.
more severe conditions, especially if it’s cracked or dry as well.
How to proceed

Regarding dehydration: Be sure to stay hydrated. The first line of treatment is to increase fluid intake because a thin tongue may indicate dehydration.
For malnutrition or other problems: A thick or swollen tongue may be a sign of various health concerns or nutritional deficiencies. For a precise diagnosis and course of treatment, it is advisable to speak with a healthcare provider if you have a persistently thick or thin tongue.