Natural Rubber / Latex

Two real issues here, both specific rather than vague. The first is latex protein allergy: over fifteen allergenic proteins in raw latex can drive an immediate IgE-mediated reaction, affecting roughly 1 to 2% of the general population and between 20% and 65% of people with spina bifida, who are repeatedly exposed through surgery and catheterisation. Reactions range from contact dermatitis through to anaphylaxis, and there is a cross-reactivity pattern with avocado, banana, chestnut, kiwi, celery and pear known as latex-fruit syndrome. The second is nitrosamines, which do not come from the tree - they form from the dialkylamine-derived accelerators and stabilisers used to vulcanise the rubber, and no nitrosamines are found in raw uncured latex. Surveys of baby bottle teats in the early 1980s, before the issue was regulated, found individual volatile nitrosamines at 22 to 281 ppb in the rubber and up to 427 ppb of N-nitrosodibutylamine in pacifier nipples, with measurable migration into milk and formula. That is now a controlled problem: UK and EU rules cap release from elastomer teats and soothers at 0.01 mg/kg total N-nitrosamines and 0.1 mg/kg N-nitrosatable substances, measured by soaking the part for 24 hours at 40C in an artificial saliva solution at pH 9. Buying teats and soothers from a brand that tests to that standard is the whole of the answer. For jar rings and cold-side gaskets, neither issue is really in play beyond the allergy.

Natural rubber tops out around 80C in continuous use, well short of silicone, and heat ages it - repeated boiling is what turns a supple teat swollen and sticky. Boiling also bears directly on the nitrosamine question: sterilising rubber teats raised the nitrosamine content measured in the rubber itself, because heat converts precursors left over from vulcanisation, although migration into milk fell with each successive sterilisation cycle. Dishwashers are hard on it for the same reason. It is comfortable at or below serving temperature, which is why jar seals and cold-side gaskets are its natural home and why kettles and pressure cookers use EPDM or silicone instead.

Natural rubber is opaque and some shade of amber, tan or milky beige, never water-clear, and it has a distinct rubbery smell straight out of the packet; silicone in the same shape is usually translucent or clear, odourless, and stays that way. Ageing is the other giveaway - natural rubber darkens, softens and goes tacky, silicone does not. Labels muddy this: "latex" on a glove box means natural rubber, but "latex" on a paint or foam can means a synthetic acrylic emulsion with no rubber in it at all, and "rubber" on an appliance gasket is far more likely to be EPDM or silicone. If a brand only says "natural rubber", ask whether it is 100% Hevea latex or a blend, and for anything an infant will mouth, ask for the nitrosamine test result.

Natural rubber has excellent tear strength, abrasion resistance and rebound, and poor resistance to nearly everything else - sunlight, ozone, oxygen and petroleum oils all attack it. Treat a jar seal or a pacifier as a consumable: months to a couple of years depending on use, not a decade. Store it dark and cool, keep oils and solvents away from it, and replace it as soon as it goes tacky, chalky or cracked at the flex points.

Vulcanised natural rubber is biodegradable in principle - it is tree carbon, not petroleum - but crosslinking and compounding additives slow that down a great deal, so throwing it on the compost heap and expecting it to vanish is optimistic. No curbside programme accepts it, so in practice it goes in the bin. It is still the only soft-part material on this site that is not a permanent synthetic polymer.