| Cover | Aug. 30, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Aug. 30, 2021 |
| Entity File Number | 000-54986 |
| Entity Registrant Name | ARCH THERAPEUTICS, INC. |
| Entity Central Index Key | 0001537561 |
| Entity Tax Identification Number | 46-0524102 |
| Entity Incorporation, State or Country Code | NV |
| Entity Address, Address Line One | 235 Walnut Street |
| Entity Address, Address Line Two | Suite 6 |
| Entity Address, City or Town | Framingham |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 01702 |
| City Area Code | 617 |
| Local Phone Number | 431-2313 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
