SEARCH CHEMICALS

Basic chemical search

The search option in the navigation bar can be used to obtain records of specific chemicals based on their names, PubChem identifiers or CAS identifiers. When the mouse pointer hovers over the search icon on the top-right of the page, the seach box opens up. By selecting anywhere on the opened search box, users can type their query into the box. Currently, the search option is limited to ONE entry only. Once the query is entered and the search is inititated, the users will be re-directed to a new page displaying the results (if any) pertaining to the input query in a tabular format containing the chemical name, chemical identifier and the literature identifier containing the supporting evidence. By clicking on the chemical name, users will be taken to the respective chemical information page.

Advanced chemical search

The Advanced Search option can be accessed by hovering over the search icon on the top-right and chosing the 'ADVANCED SEARCH' option appearing below the input box. Users can use the the advanced search option to find for chemicals based on the desired physicochemical properties or chemical similarity.

Physicochemical filter
Using physicochemical filter, users can retrieve chemicals based on physicochemical properties such as molecular weight, logP, topological polar surface area (TPSA), hydrogen bond acceptors (HBA), hydrogen bond donors (HBD), heavy atoms, heteroatoms, and rotatable bonds. Users can chose more than one filter.

Chemical similarity filter
The chemical similarity filter can be used to obtain top 10 chemicals that are structurally similar to the query compound in our database evaluated based on Tanimoto coefficient. The similarity is calculated based on either 'ECFP4' or 'MACCS' chemical fingerprints.

BROWSE CHEMICALS

Users can utilize the Browse option in the navigation bar to retrieve chemicals from TICToK. The chemicals can be retrieved based on their functional categorization in tattoo inks.

The chemical functions are broadly categorized into the following:

1. Pigments: color imparting chemicals that are insoluble in the solvent they are incorporated in
2. Dyes: color imparting chemicals that are soluble in the solvent they are incorporated in
3. Other Colorants: color imparting chemicals that were not classifiable due lack of solubility information
4. Auxiliaries : chemicals added to improve performance, stability or usability of tattoo inks (e.g., solvents, binders, stabilizers, etc.)
5. Preservatives: : chemicals protecting against bacterial contamination
6. Degradants : chemicals that are released upon breakdown of colorants
7. Intermediates: chemicals that are used in the production of colorants
8. Contaminants: unintended or unwanted chemicals present in tattoo inks

CHEMICAL INFORMATION PAGE

Chemical information page for any chemical in TICToK contains diverse information such as chemical identification and classification, physicochemical properties, predicted ADMET properties, molecular descriptors, associated hazards, regulatory coverage, associated Adverse Outcome Pathways (AOPs) from AOP-Wiki, and associated toxicological endpoints from ToxCast.

Identification

This page shows the various identifiers of the chemical, including the PubChem identifier, CAS identifier, DSSTox identifer, IUPAC name, chemical structure, SMILES, InChI, InChIKey, chemical Kingdom, chemical SuperClass and chemical Class. Users can navigate to the the corresponding chemical page on CAS, PubChem or DSSTox by clicking on the respective identifiers. The 2D and 3D chemical structures can be downloaded in various forms by clicking on the respective file types.

The page also provides the chemical classification assigned within TICToK. Clicking on the displayed classification redirects users to the corresponding browse page, enabling convenient exploration of other tattoo ink chemicals belonging to the same chemical class.

Physicochemical properties

This page shows the different physicochemical properties of the chemical.

Predicted ADMET properties

This page shows the predicted ADMET properties of chemical relevant to skin. This table can be downloaded by selecting the download option at the bottom of the page.

Descriptors

This page shows various 1D, 2D and 3D molecular descriptors of the chemical computed using PaDEL. This table can be downloaded by selecting the download option at the bottom of the page.

Associated Hazards

This page shows the presence of chemicals in exposome-relevant databases such as DEDuCT for identifying potential endocrine disrupting chemicals (EDCs), NeurotoxKb for identifying potential neurotoxicants, and ViCEKb for potential vitiligo-triggering chemicals. This page also provides the harmonised classifications associated with the chemical based on the Classification, Labelling and Packaging (CLP) Regulation (Regulation (EC) No 1272/2008) in the EU. These classifications were last obtained from the ECHA Chemicals Database on 7 June 2026. This page also provides information on associated hazards such as carcinogenicity obtained from International Agency for Research on Cancer (IARC) monographs, The United States National Toxicology Program's (NTP) Integrated Chemical Envoronment (ICE) datasets on skin irritation, REACH Dossier information on active skin/eye irritants/corrosives and active skin sensitizers, and finally the list of active and inactive skin sensitizers compiled from various resource by Golden et al., 2023

Regulatory Coverage

This page contains information on the coverage of TICToK chemicals in different regulations and guidelines.

Associated AOPs

This page shows the various Adverse Outcome Pathways (AOPs) from AOP-Wiki associated with the chemical, providing insights into potential mechanisms of toxicity. The associated AOPs are categorized based on the Level of Relevance, which is defined as follows:

1. Level 1: The stressor is associated with at least one KE within an AOP, where the KE is neither MIE nor AO within that AOP.
2. Level 2: The stressor is associated with at least one AO within an AOP, but not associated with any MIE within that AOP.
3. Level 3: The stressor is associated with at least one MIE within an AOP, but not associated with any AO within that AOP.
4. Level 4: The stressor is associated with at least one MIE and one AO within an AOP.
5. Level 5: The stressor is associated with at least one MIE and one AO within an AOP, and there exists a directed path between the associated MIE and AO.

Here, MIE stands for Molecular Initiating Event, KE stands for Key Event, and AO stands for Adverse Outcome.

For each associated AOP, the page provides information on the corresponding identifier, title, AO classification, OECD status, coverage score, and the KEs that are mapped to the toxicological endpoints associated with the chemical.

The coverage score is defined as the fraction of KEs within the AOP that are mapped to the chemical-associated toxicological endpoints.

Each mapped KE is accompanied by an information icon - ⓘ. Clicking this icon opens a pop-up window displaying the Source and the corresponding Evidence supporting the chemical–KE association. When multiple pieces of evidence are available from the same source, they are listed separately under the corresponding source. These chemical–KE associations were obtained through the manual mapping strategy described in the associated publication. The reported evidence is intended to facilitate hypothesis generation regarding potential toxicity mechanisms. Users are advised to critically evaluate the supporting evidence and exercise their own scientific judgement, as further experimental validation is required to establish mechanistic relationships.

Due to licensing restrictions, clicking an AOP identifier redirects users to the AOP-Wiki search page rather than the individual AOP page. Users can enter the displayed AOP identifier in the search box to access the corresponding AOP. In contrast, clicking a KE identifier directly opens the corresponding KE page in AOP-Wiki.

For easier navigation, a quick navigation bar is provided at the top of the page, allowing users to jump directly to AOPs belonging to a particular Level of Relevance. A floating navigation panel is also available in the upper-right corner of the page for rapid navigation between relevance levels or back to the top of the page. Additionally, a floating glossary button located in the lower-right corner provides definitions of abbreviations and commonly used terms appearing throughout the page.

ToxCast Endpoints

This page contains information on the ToxCast endpoints obtained from ToxCast invitrodb v4.2. The endpoints are categorized based on the intended target types such as RNA, Protein, Molecular Messengers, Pathway, Cellular and Extracellular. For more information regarding the assay endpoints, refer to the 'ToxCast Endpoint' file on the DOWNLOAD page.

A quick navigation bar is provided at the top of the page to enable rapid navigation between the different endpoint categories.