Although we primarily recommend using moisturizers and topical medicines for managing your itch, many of you take antihistamines to try to relieve yourself of feeling itchy. While good in theory, antihistamines have their own set of potential harms that you need to know about, especially if you’re older than age 50.
So, let’s start with some definitions. Antihistamines are very appropriately named. They’re a class of medicines that block histamine’s effects on your body. Histamine is a molecule made by lots of different cells in your body, but it’s mainly made by cells that make up your immune system. Histamine is responsible for the allergic response your body experiences when it encounters allergens or other environmental exposures. (There are also some rare histamine-driven disorders that are autoimmune or malignant in nature, in which there is an inappropriately high level of histamine in your body, leading to a lot of allergy-like symptoms. An email for the future.) Antihistamines can help with itch when your itch is caused by histamine release. However, as you hopefully have learned from this short series on itch, not all itch is caused by histamine! So, taking an antihistamine is not necessarily a good idea when your itch is not caused by histamine.
The most common antihistamines that you’ve likely taken include diphenhydramine (Benadryl®), cetirizine (Zyrtec®), hydroxyzine (Atarax®), loratadine (Claritin®), and fexofenadine (Allegra®). These are all H1 antihistamines and refer to the fact that they all block histamine 1 (H1) receptors. (There is also a histamine 2 (H2) receptor that is responsible for acid production in your stomach). We further categorize H1 antihistamines into two groups: first-generation and second-generation antihistamines. First-generation antihistamines (which include Benadryl® and hydroxyzine) have more side effects because they are lipophilic (fat-loving) and are able to cross the blood-brain barrier, where they can exert side effects on your brain (and cause grogginess). Second generation antihistamines have fewer side effects because they are less lipophilic. But, in high enough doses, they can also have side effects. Side effects from all antihistamines may include:
- Rapid heart rate and heart arrhythmias
- Drowsiness, decreased consciousness, and hallucinations
- Urinary retention (inability to pee), which may increase your risk of bladder infections
- Constipation
- Glaucoma, particularly if you take other medications that interact with antihistamines or have a history of glaucoma
The risk of having side effects from antihistamines increases when you’re older than 50. That’s because if you’re older than 50, you probably take more than one medication, and lots of medications interact with antihistamines. Antihistamine and other drug interactions can lead to both higher levels of antihistamines (leading to more antihistamine side effects) and higher levels of other drugs in your body, which, as you can imagine, can cause a host of other problems.
Not only that, but an unfortunate fact of aging is losing muscle mass, while gaining body fat. And, antihistamines, especially the first-generation ones like Benadryl®, accumulate in fat (remember, they’re lipophilic)—so, if you’re older than 50, you’re at a greater risk of having higher concentrations of antihistamines if you’re taking these on a regular basis. Translation: more risk of side effects. And, importantly, if you’re taking Benadryl® regularly to treat your itch, you’re putting yourself at risk for a hip fracture due to medication-induced drowsiness. Hip fractures in old age can be life threatening.
So, what to do if you’re older than 50 and think you would benefit from taking an antihistamine? Well, if you have itch that’s histamine-driven, you probably would benefit from taking an antihistamine. The literature suggests that Allegra® (fexofenadine) is the best option because even at really high doses (like twice the licensed dose), you still won’t experience sedation or grogginess. And, it’s safer than Zyrtec® (cetirizine), which can cause drowsiness, even though it’s a second-generation antihistamine.
As always, our recommendation for itch in general is good skin hygiene, which looks like:
- Not taking hot showers
- Showering for 5 minutes or less – the longer you shower, the more you strip your skin of its barrier oils
- Using non-harsh, gentle, pH balanced soaps (more on that to come later)
- Using a great moisturizer every day to ensure that your skin barrier functions at its best (we know of one)
Hope you learned something useful for yourself and/or your aging parent!
Reference
Grinnell M, et al. Antihistamine safety in older dermatologic patients. J Am Acad Dermatol 2022; 87:381-6.