Imaginary, air-carried attractant exohormones/ pheromones.
It's a word used mainly in 'sniff therapy', a new psychotherapeutic method for couples with sexual problems, where -- basically 'sniffing' your partner's undies can fire up one's IRMs (innate releasing mechanisms: the brain-prewired mechanism for receiving chemical pheromones!).

These undetectable pheromones are thought to play a major part in what has been called the 'addiction factor': the headiness, memory and attraction caused by your partner's smell, which might play a significant role in the affinity you might have lost from either way too much 'partner familiarization' or, long-timed loss of contact!

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