Final answer:
In type I hypersensitivity reactions, histamine from mast cells causes vasodilation, mucous gland stimulation, and tissue swelling, but not enhanced sebum production.
Step-by-step explanation:
During a type I hypersensitivity reaction, histamine released from degraded mast cells causes several effects, but it does not enhance sebum production.
The effects of histamine release include vasodilation, which leads to increased blood flow and redness, mucous gland stimulation, which causes runny noses and watery eyes, and tissue swelling (edema), due to increased fluid in the tissues. Enhanced sebum production is not a result of histamine release in type I hypersensitivity reactions.