Cross-Reactivity: Why an Allergy to One Botanical Might Mean Avoiding Others

If you’ve recently had patch testing, you may be wondering: if I am allergic to one fragrance or plant ingredient, do I need to avoid them all?

The usual answer is yes, but it’s a little more nuanced than that. Understanding how fragrance and botanical allergies relate to one another can help your provider determine which ingredients to avoid without unnecessarily restricting your choices. 

Two Important Concepts:

When dermatologists interpret patch testing, two patterns are considered:

1. Cross-Reactivity: This occurs when the immune system recognizes two different substances as similar because of shared chemical structures.

2. Co-Reactivity: This occurs when a person reacts to two molecularly distinct allergens, not due to chemical similarity, but because individuals are commonly exposed at the same time. 

A common example of coreactivity is neomycin and bacitracin, two antibiotic ointments that are chemically unrelated; however, frequently combined in over-the-counter triple antibiotic ointments. 

Why Fragrances and Botanicals Are More Complicated:

Fragrances and botanicals can be particularly challenging in the evaluation of skin allergies. Unlike many substances tested in patch testing, which are single well-defined chemicals, fragrances and botanicals are typically complex mixtures made up of many different chemical components. Adding to the complexity, most personal skincare products contain blends of multiple fragrances. Many products simply list “fragrance” on the ingredient label, without specifying the individual components. This lack of transparency makes it difficult for consumers to identify which specific ingredients may be responsible for a reaction.

As a result, when a patient has a positive patch test to a fragrance or botanical allergen, the most cautious recommendation is often to avoid all fragrances altogether. However, emerging research offers some optimism and may allow for greater flexibility in personal care product selection. To better understand these relationships, researchers examined how often certain fragrance and botanical allergens “travel together” (aka: how frequently patients test positive to both).

What the Research Shows: 

In a recent publication by Mayo Clinic, researchers analyzed patterns of co-positivity among fragrances and botanicals. In other words, they examined how often patients who are allergic to one fragrance may be allergic to another. 

This type of analysis helps identify “clusters” or groups of ingredients that commonly react together.

The Following Fragrance and Botanical Co-Positivity Clusters Were Identified:

For example, if a person is allergic only to the plant materials found in Group 2 (Compositae mix, sesquiterpene lactone, and parthenolide), and not to other fragrance allergens, they may not need to avoid all fragrances.

Plants included in Group 2 are members of the Compositae (Asteraceae) family, such as daisy, chrysanthemum, and sage. Individuals allergic to these plants may develop a rash with direct exposure to the plant itself or products containing extracts.

However, if someone is allergic exclusively to the Group 2 plant allergens, and not to other fragrance components, SkinSAFE can filter out products containing those specific plant ingredients. This allows patients to safely choose from a broader range of fragranced personal care products that do not contain the relevant botanical allergens.

On the Other Hand, Some Fragrances/Botanicals Were Found to Less Commonly Co-React:

Although not currently possible,  SkinSAFE is exploring the ability to help individuals who are allergic only to specific fragrance ingredients identify products free of just those components. However, this approach depends on complete ingredient transparency, meaning that all individual fragrance components must be disclosed on the product label, which unfortunately is not common practice.

Another example involves individuals who test positive to certain fragrance allergens but are not allergic to Balsam of Peru (Myroxylon pereirae), sodium benzoate, or benzoic acid. In that case, SkinSAFE will give you options for products that have benzoic acid. This can give your skin care products a soft, pleasant, balsamic odor. It is naturally found in many fruits and spices (like cranberries and cinnamon), which gives it a slight "sweet resin" quality. 

Why Patch Testing Co-Positivities Matter:

Many patients are tested to a relatively small standard panel of fragrance molecules rather than a broad array of fragrances and botanicals like the 40 that are tested at Mayo Clinic. Because of that, your results may not tell the entire story. Understanding co-reactivity patterns can help. So, today, for someone allergic to a fragrance on patch testing, the most cautious approach is to avoid all fragrances. Keep in mind that products marketed as “Fragrance Free” or “Unscented” often do contain fragrances, so checking products through SkinSAFE is strongly recommended.  

That said, there may be more flexibility for certain individuals. For example, patients who are allergic only to select plants in the daisy (Asteraceae) family, or those who are fragrance-allergic to components outside the Balsam of Peru family, may have options that still contain a scent. Your provider can help determine which related ingredients should be avoided and which may still be safe for you to use.

The Bottom Line:

While the most cautious approach for many fragrance-allergic patients is to avoid all fragrances, a positive patch test to one fragrance or botanical does not automatically mean every scented product is off-limits. By understanding patterns of co-reactivity, allergy management can be more precise, practical, and tailored specifically to you. 

Resources:

1. Yang YW, Yiannias JA, Davis MDP, Hall MR, Voelker DH, Youssef MJ. Evaluating Copositivity Patterns in Fragrance/Botanical Patch Testing through Hierarchical Clustering and Network Analysis. Dermatitis. 2026 Jan;37(1):61-67. doi: 10.1089/derm.2024.0442. Epub 2026 Feb 6. PMID: 40533092.