While peeling purple yam / ube for the maja recipe, I felt a mixture of uncomfortable skin itchiness. After, I immediately washed my hands with soap and water. The itchiness persisted for about 15 minutes after washing.
I learned later that acidic solution like vinegar, calamansi juice and lemon are effective for immediate relief.
I asked Mr. Web, “How to prevent skin from getting itchy while peeling ube?” I got no answer. The yam should be cooked well to eradicate the harmful substance. It could cause harm when eaten raw or insufficiently cooked.
I got hint, the substance that causes itchiness is degraded by heat.
Perhaps the culprit substance is more concentrated near the peel. Remember that nutrients are more concentrated near the peel. The same might apply to harmful substances. I got a piece of raw purple yam. I rubbed the center part to my right arm. I got a piece of skin and rubbed it to my left arm. The left arm felt intense itch while the right arm almost felt nothing. It is really concentrated near the peel. Perhaps dipping in hot water for few minutes is going to solve the problem.
I prepared four chunks of raw ube. I got a casserole with water and bring it to slow boiling. I dipped the first chunk for one minute, the second for two minutes, the third for three minutes and the fourth for four minutes. Then I got peels from each chunks and rubbed each to different parts of my left arm. I felt a minimal and negligible itchiness. I noticed no difference among four chunks.
update as of May 2017
I recommend blanching or completely cooking the root prior to peeling.
Thanks to Dr. Pri Bandara for mentioning the saponin. I did a little digging myself and found out:
Yam contains diosgenin saponin and dioscorine alkaloid. Toxic compounds that can be removed by washing, boiling and cooling. It was also mentioned that high level of alkaloids causes itchiness and bitterness.
Tropical Agricultural Research & Extension 15(1): 2012
PROXIMATE ANALYSIS AND PHYTOCHEMICAL AND MINERAL CONSTITUENTS IN FOUR CULTIVARS OF YAMS AND TUBER CROPS IN SRI LANKA
Senanayake SA, Ranaweera KKDS, Bamunuarachchi A and Gunaratne A 1Department of Food Science and Technology, Faculty of Applied Sciences, University of Sri Jayewardenepura, Nugegoda, Sri Lanka Department of Agriculture, University of Sabaragamuwa, Belihuloya, Sri Lanka
Article accepted: 22 March 2011