Aloe vera is widely celebrated for its moisturizing and calming properties, making it a staple for soothing sunburns and minor skin irritations. Paradoxically, many people report that applying aloe vera gel results in an immediate, uncomfortable stinging or burning sensation instead of the expected relief. This unexpected reaction is not a failure of the skin, but rather a complex interplay of the plant’s natural chemistry, commercial manufacturing practices, and individual physiological responses.
Natural Chemical Irritants in the Aloe Plant
The irritation often begins with the aloe plant’s natural defense mechanism, which involves a bitter, yellowish liquid called latex. This latex is found in specialized cells located just beneath the green outer rind of the leaf, not the clear inner gel. When a leaf is cut, this exudate seeps out and can mix with the inner gel if not properly drained.
The primary irritants within this yellow latex are anthraquinones, with aloin (also called barbaloin) being the most prominent. While aloin is known for its laxative properties when ingested, topical application can trigger contact irritation, leading to redness and a stinging sensation. This irritating nature is the fundamental biological reason for a burning feeling from raw or poorly prepared aloe.
The Impact of Commercial Processing and Purity
The quality of the final product plays a substantial role in whether an aloe gel soothes or stings the skin. Pure, therapeutic aloe vera gel comes from the inner fillet of the leaf and must be separated from the irritating outer rind and latex layer during processing. Manufacturers using a “whole leaf” extraction method without adequate purification risk including residual anthraquinones like aloin in the final product. The International Aloe Science Council recommends that topical products contain aloin levels of 50 parts per million (ppm) or less to ensure comfort.
Beyond the plant’s inherent compounds, the additives in many commercial gels can also cause irritation. Many products contain drying alcohols, such as isopropyl or denatured alcohol, added to create a quick-drying, cooling sensation. While initially refreshing, these alcohols strip the skin’s natural barrier, resulting in dryness and stinging, especially when applied to compromised skin like a sunburn.
Additives and Preservatives
Other common irritants are added for aesthetics or preservation, including synthetic fragrances, artificial colorants, and certain preservatives. Bright green dyes are frequently added to make the product look more “natural,” but these dyes are unnecessary and can sensitize the skin. Preservatives like parabens, Triethanolamine (TEA), or formaldehyde-releasing agents are used to extend shelf life but are known contact sensitizers that can provoke irritation and stinging.
When Stinging Signals an Allergic Reaction
While chemical irritants and additives cause non-allergic irritation, a stinging response can also signal a true physiological allergy in some individuals. This is a Type IV contact dermatitis, which is a delayed immune system reaction to specific proteins in the aloe plant. True allergic symptoms are usually more severe and prolonged than the temporary sting caused by a poor-quality product.
A genuine allergic reaction often manifests as significant swelling, intense and prolonged itching, the development of hives, or blistering at the application site. Although an aloe vera allergy is uncommon, affecting only an estimated 0.1% to 1% of the general population, it requires immediate cessation of use.
Applying any substance, even pure aloe gel, to severely damaged skin, such as deep burns or open wounds, can intensify the burning sensation. This occurs simply due to the compromised integrity of the skin barrier.