Some are alkaline as well. But, right now, we are talking about citrus fruits and they are acidic so let us look at the pH values of some widely available fruits to know which can be used safely on skin and which should be avoided. Though, lemon is the most loved citrus fruit.
Most Acidic Fruits Tangerine - 3.90, Grapefruit - 3.38, Lime - 2.40, Lemon - 2.30 Least Acidic Fruits Mandarin - 11.50, Orange - 4.35, Kumquat - 3.95 Also, remember that as the fruit ages, its acidity decreases.( Source )
Now, the pH level of the skin around 5.4 so if you use orange instead of lemon, its more gentle on skin. Even I was surprised to know that mandarin is alkaline and not acidic. When I was writing this post, I was reminded that I prefer tomatoes to lemon so checked its pH value as well.
pH value of fresh tomato ranges between 4.3 and 4.9 ( source ). In fact, potato is also considered to be great for skin. Its pH value lies between 5 and 6.5 which is relatively very less acidic and more gentle on skin. So, you can now customize your home remedies according to the pH levels of the ingredients :)