Eucalyptus can have some side effects, depending on how you use it.

Eucalyptus oil is toxic if swallowed. Even small amounts can cause nausea, vomiting, diarrhea, dizziness, and seizures.

Ingestion

Applying undiluted eucalyptus oil to your skin can cause irritation, redness, and itching.

Skin irritation

Eucalyptus can cause allergic reactions in some people, including symptoms like rash, wheezing, and difficulty breathing.

Allergic reactions

Large amounts of eucalyptus oil can slow down your breathing and nervous system function.

Central nervous system effects

Eucalyptus oil may interact with certain medications, such as blood pressure medications and medications for breathing problems.