What is a possible consequence of vomiting?

Vomiting can lead to dehydration as it causes the expulsion of fluids and electrolytes from the body. When a person vomits, they lose not only the contents of their stomach but also vital fluids that are necessary for maintaining hydration levels. This loss can result in symptoms such as dry mouth, decreased urine output, and increased thirst, which are characteristic signs of dehydration.

The other options do not directly stem from the act of vomiting. For instance, while vomiting could lead to intake of excess fluids if someone tries to compensate, this is not a direct consequence of the act itself. Allergic reactions are immune responses and are unrelated to the process of vomiting, while headaches, although they can occur after vomiting due to various factors (like dehydration or tension), are not a direct or guaranteed consequence. Hence, dehydration stands out as the primary consequence of vomiting.