Despite their nutritional similarities, green and yellow kiwi differ slightly in taste, texture, and the sensation they cause when eaten, especially regarding the peculiar "itchy" sensation that remains on the tongue and that is popularly associated with green kiwi.
The explanation for this phenomenon lies in the raphides, cellular structures in the form of small needles made up of calcium oxalate crystals, which are present in both types of kiwi. These raphidia can cause slight irritation or abrasion to the mucous membranes of the mouth, resulting in the itching sensation experienced by some people. A TikTok user, @bajo.elmicroscopio, has shared microscope images showing the presence of raphidia in both types of kiwi, thus disproving the belief that only green kiwi causes an itchy mouth.
People might perceive green and yellow kiwis itch differently because of each variety's level of sweetness. Yellow kiwis are generally sweeter and less acidic, which could attenuate the irritating sensation caused by the raphides. In contrast, the green kiwi's higher acidity could intensify the perception of itchiness. Thus, the contrast in the sensory experience between the two varieties of kiwi is not due to the absence or presence of raphides, but rather to how the flavor profile of each type interacts with these microscopic crystals in the mouth.
Source: larazon.es