How to automatically remove duplicates from a list in Excel?
In Excel, we can use the Remove Duplicates feature to remove the same values from a list, but is there any trick to automatically remove duplicates from the list? In this article, I introduce the tricks on automatically removing duplicates if a duplicate appears in a specific Excel column.
Auto remove duplicates from a list using Data Validation
Auto remove duplicates from a list using Kutools for Excel 
Auto remove duplicates from a list using Data Validation
1. Click Data > Data Validation. See screenshot:
2. In the popping dialog, under Settings tab, select Custom form Allow list, and type the formula =COUNTIF($A$1:$A$20,A1)=1 into the Formula box. See screenshot:
In the formula, A1:A20 is the range you want to auto remove duplicate from.
3. Click OK. And now if you type a duplicate value, a warning dialog will appear.
Auto remove duplicates from a list using Kutools for Excel
If you are not familiar with formulas, you can apply Kutools for Excelās Prevent Duplicate utility to stop from duplicates being typed in range at once.
Select the range or a column you want to auto remove duplicates, and then click Kutools > Prevent Typing > Prevent Duplicate. See screenshot:
Some dialogs appear to remind you of certain notices, click Yes > OK to close the dialogs.
Now a warning dialog pops out to remind you when you try to enter duplicate values.
Here is another relative utility called Prevent Typing, you can specify the character you want to prevent typing or only allow typing in a list as below screenshot show:
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Demo: Auto Remove Duplicates Entries using Kutools for Excel
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