Benadryl can help with swelling, but only if the swelling is due to an allergic reaction.
How Does Benadryl Help Reduce Swelling?
Benadryl, a brand name for the drug diphenhydramine, blocks the activity of histamine at a type of receptor called the H1-receptor. These are found throughout the body in your blood vessels, skin, nerves, and organs. When you have an allergic reaction to something, including foods, chemicals, insect bites/stings, poison ivy, etc, your body is targeting whatever it has identified as “not you.”
As part of this process, special cells called mast cells release packets of histamine they were storing, causing your blood vessels to expand, and allowing immune cells to pass through tissues more easily to get to the source of the intrusion.
Think of it as an ambulance, which helps first responders to get to patients and hospitals faster by clearing the way a bit. Now imagine that ambulance occasionally picks up random people walking on the street and rushes them to the emergency room, because they “look sick”. That’s basically what happens with allergic reactions…the body has decided (often inappropriately) that Substance A doesn't look too good, and it needs to get it out at all costs.
Anti-histamines For Allergic Reaction Swelling
You may experience this as swelling (wheal and flare), itching, hives, or rashes. If that’s the issue you’re trying to treat, Benadryl will likely help; it isn’t the best choice though, due to the strong side effects and sedation it causes.
Newer antihistamines like Claritin (loratadine) and Allegra (fexofenadine) may be better options, as they don’t cause sedation.
Zyrtec (cetirizine) is another option, but it sometimes causes sedation as well, just less than Benadryl. If the issue is on your skin, topical Benadryl can be very effective without the unpleasant side effects. Topicals are also a safe way to manage skin reactions in the elderly and children under 6, as oral Benadryl is not recommended for these patients unless prescribed by a doctor.
With any of these options, be sure to check with your physician and pharmacist if you have any medical conditions or take other medications regularly.
Now, allergic reactions are certainly not the only cause of swelling; swelling often occurs due to inflammation and fluid buildup around injured joints, impact injuries, as well as cuts, scratches, or abrasions. Antihistamines like Benadryl are not reliably effective ways to manage symptoms of these issues, as the body’s inflammatory response to these injuries uses different sets of chemicals, and histamine takes a backseat to them.
It is unclear if antihistamines have any effect on the inflammation seen in acne symptoms.
Allergic Reactions Emergencies
If you’ve read this far, I’m assuming your swelling is annoying and uncomfortable, but not an emergency. However, if you are having or have ever had a severe reaction or swelling to anything, especially if you had trouble breathing, you may be experiencing anaphylaxis.
Anaphylaxis is a serious medical emergency that can result in death from airway blockage if left untreated. Benadryl alone is not an appropriate or effective treatment for this, although it may be given as an add-on to the main treatment for anaphylaxis, epinephrine.
Benadryl in any form, though, is never a substitute for epinephrine. So, if there is swelling of the face, tongue, or lips, or any difficulty breathing (like wheezing, whistling, rasping), especially if the cause is not obvious, it's critical that immediate medical attention (meaning call 911) be sought for the person, whether it’s happening to you or someone else.